English spelling errors are common because English is not written phonetically. If you fix that, you reduce the errors, not increase them. Spelling mistakes would still occur to some degree (ultimately because one dialect's pronunciation must be chosen for the written standard) but it would still be an improvement.
Imagine if anglophone students could learn to read and write in 2 years like their peers in Spanish and German speaking countries (many dozens of others) instead of 10.
It is not incorrect.
True, that is perfectly in line with what I said and contradicts the statement that he "made changes. "making changes" is not the same thing as "marking major shifts".
Many would imitate his style. But we also know very little about the styles that influenced Shakespeare. New mechanics? Not sure what you mean by that. He did not alter the grammar of English nor did he invent words. When people claim he "invented" words or phrases, what they really mean is that his works are the first recorded example. That is not the same thing as "inventing."