Dystopia

I generally try to use anything that isn't meta, and is really like weapons with a unique trait/gimmick. The Hystrix is a secondary I've been using a lot more because you can cycle through an element to force proc heat/cold/electric/toxin, which is really useful for different setups like heat if you want to use Cascadia Flare or cold if you're trying to boost crit damage/slow demolysts without interfering with your modded elemental combos. It does have a fairly small magazine,so it can be harder to use without some form of ammo efficiency/infinite ammo.

Dystopia–not our one

Should probably get this out of the way now, wouldn't be surprised if it comes up fairly often, but I'm a different person from the one you're talking about. It's just a name I used years ago in a different game and I reused it when I made my warframe account.

Limbo works for going through Lua spy vaults and I think corpus green lasers. There are still much better choices though. I typically just use Wisp because I'm invisible as long as I'm airborne and I can teleport to the 2 to bypass lasers.

Limbo has a bit of a learning curve and is also one of those frames where it's very hard to be good Limbo.

Playing in a group has an impact has an impact on enemy density and also has an effect on how often enemies will target you (some behind the scenes stuff limiting how many enemies can attack at once). Enemy level does not scale with the number of players in a lobby.

Most game modes are generally better in public, sometimes you can end up in lobbies where people have "disruptive" builds like a max range Wisp slowing down enemy pathing in a defense mission. You do get more drops due to more enemies being able to spawn, and when you start doing fissure missions, anyone that manages to collect 10 reactant before extracting is able to pick one of the rewards from the opened relics. If you fail to collect 10 reactant before extracting, your relic will not be consumed but you also wont be able to pick a reward from the pool of cracked relics.

Less popular game modes like Infested Salvage actually go by faster if you're playing solo, the mission length scales with player count.

The main uses for Operator/Drifter are for certain bosses, utility and for killing special enemies that have two phases like Vomvalysts and Thrax. The most useful focus school for new players would be Zenurik. You want to unlock Wellspring which lets you create a marked zone by pressing 1 (assuming you're on PC) and standing inside it with your warframe will give you an energy regen buff. There are some other quests that do make use of your operator/drifter too, and a game mode focused around playing as the Drifter (Duviri: Experience - feels very different from base warframe though and controls could be a little less clunky).

If you didn't pick Zenurik as a starting school, you can find 'Zenurik' Focus Lenses them as a potential reward in Cetus Bounties at Konzu. (These reward tables rotate so they won't always be available). They can be installed on any piece of equipment that is rank 30 by going to Arsenal > [pick any piece of equipment that is rank 30] Upgrade > Actions (at the bottom of your screen) > Focus Lens. This will convert a portion of affinity gained to Focus which can then be used to unlock a new Focus school once you have 50k points accumulated within the respecitve school. Warframe is unfortunately a little convoluted, you want to make sure you're using an Zenurik lens if you're trying to unlock that Focus school. Just play the game and you will gain standing passively.

To change your focus school, Esc > Equipment > Operator > Focus > Pick a school to swap to/unlock if you have enough points in the specific school you want. *You might be able to convert Eidolon Shards as an alternative to farming focus but this is later progression wise, I think you might still need to go through initially unlocking a specific school using it's respective lens.

*I'm mostly going off memory, if you don't have access to operator yet by pressing '5', it's currently only enabled for quest progression. It becomes useable in game after completing 'The Second Dream'.

You're also at the point where you can start working on your operator. You want to enter the Plains of Eidolon at night (Set match making to solo to avoid randomly getting put into a public Eidolon/Tridolon hunt), and you can kill Vomvalysts for their cores, and find Cetus Wisps which spawn near pools of water and appear on your map as an item icon. They can also be given as a Cetus Bounty Reward if you don't want to do laps around the map, and you'll get other useful rewards from doing bounties. Probably best to stick to the lower level ones, nothing prevents you from accidently selecting a mission with enemies above your level range.

Find the Quills in Cetus to trade in the cores for standing to rank up their syndicate and purchase the parts for your first amp. Anything is better than the mote amp, but the first amp you will make will probably use the Raplak Prism, Pencha Scaffold and the Clapkra Brace. Most of the resources needed to craft these components are found on the Plains of Eidolon by fishing/mining. Amps crafted this way are modular items and will require you to take the crafted components back to Onkko to assemble them. Amps can be leveled to 30, and then brought back to Onkko to be guilded. This lets you name your amp, colour it, and put arcanes into it (not relevant for your current progression but does become important later on). To change your amp, go to your orbiter* Pause > Equipment > Operator > Equipment, and you should see the option to equipt another amp. *Should also be able to do this from any of the open world hubs, not an option in relays.

If you talk to Konzu at night, you will see the Eidolon Bounties available. At your current level it is probably best to avoid them. The first Eidolon will be doable in a squad but I still think think it's probably too early for you've currently progressed. It is a good source of items to trade for standing with the Quills though.

If you're having trouble finding them, you should be able to fast travel there from the pause menu. You will see a stone door there, use operator mode to enter it. If you don't have the option to fast travel there, you want to start from the gates and hug the left wall and go up a staircase until you find a stone wall, and use operator mode to enter it.

Warframe's early game is a bit of a mess balance-wise, and has very little guidence.

Make use of nightwave for some useful Aura mods, and you can get some weapon/warframe slots for ranking it up. Any challenges that aren't completed by the end of the week just get banked and become available again once you've completed some of your current week's challenges. The weekly challenges never really expire until the end of the current nightwave cycle which tends to go on for quite a while. You can purchase Orokin Reactors/Catalysts from nightwave to increase your warframe/weapon mod capacity to 60 (for a rank 30 warframe/weapon). I don't think I would really want to use many of them on a base warframe/weapon, you're better off using them on a Prime instead/or if there's a base warframe/weapon you tend to use often. Once you progress further into the game, you usually have more Reactors/Catalysts than you can use.
Forma is the other way to fit more mods into your warframe/weapons, a little build restricting because they need to match the polarity to reduce the mod cost (or penalty if it's a different symbol), but that's where the min-max fun is if you're into making builds.

If any build guides suggest "Galvanized Mods" or weapon arcanes, then you're looking at a guide aimed more for very late game. Modding generally follows the same pattern for all weapons, Base Damage, Crit Chance, Crit Damage, Multishot, Element, Optional/QOL.

For a primary weapon you want:
Serration, Point Strike, Vital Sense, Split Chamber and your other mod slots are for an elemental combo/option mods (reload speed, fire rate, etc). You might have noticed a planet will suggest an element type like Viral, you would go into the mod screen for your weapon and type in "Viral" into the search box and it will filter mods that can be used to make that element.
Secondary Weapons: Hornet Strike, Pistol Gambit, Target Cracker, Barrel Diffusion, element and optional mods. Melee: Stance Mod, Pressure Point, Organ Shatter, True Steel, element and if your melee weapon is slow then you will want a mod like Fury on to increase the attack speed, otherwise this mod falls under the optional category. If you have the Skijati, that weapon comes with the Sacrificial versions of point strike/organ shatter along with the polarities to use those mods, so use those instead of their base versions.

One last thing is if you haven't joined a syndicate yet, pick one and rank it up. Either pick New Loka, Perin Sequence and Red Veil OR Cephalon Suda, Arbiters of Hexis and Steel Meridian. Someone probably can probably do a better explanation on how these syndicates work than I have time to write right now/there should be existing guides which should be able to explain how they work in a much less confusing way than I would explain it.

MCGamerCZ has a fairly good overview for lich missions if you want a refresher on how kuva lich missions work. They're more of a mid/late game type of mission. If you can do early steel path missions/have incarnon weapons, then hunting a lich shouldn't be too difficult for you. I would avoid Toxin/Radiation liches until you know what you're doing because they can enable friendly fire which is usually ends up with your team nuking themselves/the objective. The other variants shouldn't cause you any trouble though.

Some people will avoid stabbing their lich until they have all the requiem mods unlocked to keep it as low level as possible. If a lich is downed 3 times without being stabbed it will flee. Another thing you can do is just use a warframe which can go invisible and just melee it until it dies.

A really niche relic farm, some relics for the most recent primes can be found in Profit Taker bounties.
Check Profit Taker Phase 2, 3, and 4 bounty rewards, these missions are fairly short and have a reasonably good drop rates for their respective relics. You can open Nightwave/view lich to skip dialog gated parts of the quest.

Just some rough estimates for times:
Phase 2 ~2min
Phase 3 ~5min
Phase 4 3-5min

For phase 2, any speedrun warframe like Wisp/Nova/Wukong. Bring along a Shade or Huras Kubrow for their stealth ability. Best to play this mission solo, I find the game likes to load me into lobbies after the mission reward screen if I'm playing public.

Phase 3 only requires you to match the Profit Taker's element, more damage does not speed this up. Use whatever you're comfortable with.

For phase 4, use Chroma or any tanky warframe with Eclipse/Roar. Knockdown immunity (overguard/passive/ability) is nice but not a requirement. *If you find you aren't seeing a bounty reward screen, the Profit Taker is taking too much damage from a single shot in one of the archgun phases, try switching to the Imperator/Mausolon.

These missions are mostly just an alternative to playing a mission like Disruption/ESO. The tradeoff is that you don't really get burner relics but any relics that you do get will be radiant. The other nice part about playing these missions is that you don't need to deal with waiting for the right rotation for your desired relic to become available.

If you need a weakened version of one of the infested companions, you can use the Tranq Rifle (sleep arrows only temporarily put them to sleep, Tranq Rifle is infinite duration) to put them to sleep and then attract an infested to the area to attack them. I would use Ivara to go invisible once the infested are alerted, If you're brining a companion for something like enemy radar, it should be a sentinel without a weapon so that it can't accidently kill the infested before it converts the Predasite/Vulpaphyla to their weakened version. Look up the cycle needed to spawn your desired variant or try your luck with Pheromones.

The last thing is if you can do is work on multiple things at the same time like rank up weapons/companions while collecting relics like in ESO to make things a little less grindy. Passively get relics through spending syndicate standing, or while cracking relics in the void. There's a chance someone runs a relic you need and this can end up saving you a lot of time. And take breaks whenever you need them, there's no reason to burn yourself out just to reach some mastery rank.

Survival techniques/tools would be helpful. It could also just be me being too used to Limbo before the eximus rework, and using the rift as a "panic button" expecting to be safe from eximus.

Dealing with eximus/over guard units seems like it would be a pain, especially for how squishy he is and not really being safe in the rift anymore.

Styanax was pretty fun to play, I had it modded to be a shield tank before his Final Stand augment was added, so he had pretty good survivability. His 1 without his augment feels terrible to use though because it requires you to hit a target to group enemies and if that enemy has Overguard it won't group any of the other enemies around even if they aren't protected by Overguard. It doesn't help that Overguard is getting put on everything in recent updates, his augment does let you hit the ground instead but that feels more like a band-aid instead of just letting it group enemies that aren't CC immune.

He had pretty good energy management with rally point and tharros strike helped with removing armor from tankier enemies before killing them to replenish your shields. I don't think Final Stand was useful on its own, but it is a very good ability if you're using its augment.