What are the requirements from immigration? I believe I need to be able to prove the money comes from abroad, but what restrictions does that entail specifically?  Can I use something like Transferwise? Thanks!

Removed an off-topic post.

Best for myself would be a SWIFT transfer to one of my Thai bank accounts.

Can use Wise, need a Bangkok Bank or Kasikorn account for transfer to be shown as International, if that's required, must select reason for transfer "long term stay"

I don't think the money needs to be proven from international sources. UbonJoe may be able to confirm.

You do not need proof the 400k baht required for a non-o visa or one year extension of stay based upon marriage came from abroad.