The TM30 is a "Now" document, but the problem will be with the certificate of residency as I don't believe immigration will allow one with a hotel address, and the certificate is actually posted to the address
All the things you want to do you will most definitely need a TM30. A quick fix is to book a night at a hotel and get the screenshot printout from there
Unfortunately Thai immigration don't do "introvert". You can do learning online but not with an ED visa. You can get the 60 day tourist visa, which you can extend a further 30 days. There's nothing to stop you signing up online under this visa
It's difficult to get an ED visa for online language tuition. You can do online anywhere in the world, why would you need to be in Thailand? Language schools have certain stipulations which include a minimum hours/days per week class attendance, and your language skills will be tested by immigration when you go for extensions.