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.