Now it's a matter of sustaining and slow growth. Hopefully. Best thing you can do to see Lemmy succeed is participate: comment, post, doomscroll All+Top Hou ;)
It'll take a while for some of the smaller communities to get critical mass. And that's okay, probably. Critical mass is here for the larger topics already. I'll do my best to help :)
I think the 90% assumption only holds true after some time. Because right now Lemmy is still the hot new thing which means that probably more than 10% of the people are active. Although that is probably changing right now as indicated by your graph.