Most of what you're asking is Embassy specific, 3 months is generally enough, if you can show you have a portfolio and client list and appear genuine. A lot of it is having a brief convincing cover letter. As far as bank statements there are 2 different types, the 500k funding, and the freelance income payslips/deposits/ whatever related to your contracts/gigs. On top of that a tax return might be requested, in your case of only being viable 3 months it's moot. Again, it's up to you to provide a convincing application with a brief cover letter explaining how your situation and documents either tick off the boxs, or the reason why it doesn't.
You said partner, so I imagine it's not a legal marriage. Regardless, yes you can employ them and create a contract and employment certificate stating that they can work remotely specifically in Thailand. They will need 500k baht in a bank account in their name.
many schools prefer a certain accent for their students. Personally I find some accents hard to understand, even British or Aussie, many Indians seem to have a general higher base level tone which alters the genuine sound of the language. Some Indians have a very neutral accent and tone, probably educated overseas.
Yes it's possible to return for another 60 day stamp, you can also extend the current free visa exempt entry stamp another 30 days at immigration for 1900 baht