Most likely the reason why Stuart asked about the office and your nationality is that the Non-O should not have these as requirements, but they are requirements for Non-OA Visa

It can be any transfer, but ensure that the Thai bank shows it as an international transfer

@Stan *****

yes, just apply for that visa, based on retirement, in the US

@Greg ********

no you still seem confused. The initial visa, you apply for in your home country normally, is 3 months and you show your local bank information. You them apply for the 12 month extension when you are in Thailand. When you arrive in Thailand on the Visa you should open the Thai bank account and transfer the 400,000 Bhat into it. I believe it needs to be there 2 months prior to the application for extension

@Greg ********

as Brandon said you need to show the funds in the Thai bank when applying for the extension. I recall that it is 400,000 Bhat for 2 months as opposed to the extension of stay for retirement which is 800,000 Bhat for 2 months.

@Eric *******

this is incorrect, if you have a visa then you would open the bank account in the first 30 days and put in the money. Then you apply for an extension of your visa, not for a new visa. You have to have the money in the bank account for 60 days.....your visa would be for 90 days so that is why you have to open the bank account within 30 days.

Are you on Thailand now and, if so, when did you enter?

Just beware that advice/information about Thailand's regulations and procedures given now for an event that is happening in 3 years may not be particularly relevant when you are ready to start the process. I understand the desire to feel comfortable about something, but if possible just relax and as you come up to that 6 month mark you can check/ask and get feedback that will reflect better the reality you will be dealing with.