You can prove your income from your bank statements for getting your non-o visa from your home country. However, you have to have the 800k in a Thai bank account 2 months prior to your 1yr extension. The only way around this is to pay an agent to bribe an immigration officer. Works until it doesn't.
if you apply abroad, you only need the money in Thai bank 2 months before extension application. Dollar has gone up some in the past few days. Note that on 800k, the 2฿ exchange rate difference amounts to $50.
I don't think money has to be seasoned for application. It does for the 1yr extension. And I don't believe that money needs to show as international transfer, just that it's there. I can't answer about the bank branch because so many times here, when I try to use logic, I'm wrong! 😁