I asked the same question a few weeks ago. The answer, which may depend on the individual Immigration Office, was to move ฿40x,000 to the new account first, then the other ฿400,000 a week later.
Of course you do this outside of the required balance periods.
In my case I was looking for a higher interest rate.
Just get the Non O from the Thai embassy in the UK.
Come live here for all the seasons to make sure you enjoy it as much as you believe before fully committing.
Pai is very small and can be boring. Chiangmai has much more, including an international airport to go to Vietnam or Phuket for the burning season.
I retired here quite comfortably on about $25k USD annually. Half that might be a bit of a struggle to bank your visa money, buy a vehicle, insurance, and have an emergency fund, especially to drink and eat out.
You can easily take $10,000 or even $1,000,000 USD or more from USA to Thailand.
It can be a cashiers check, cash, gold or negotiable instruments.
The only requirement is that you must declare values over a certain amount to customs agents at both borders.
In your case $10,000 USD to US and $20,000 USD in Thailand.
You will want a paper trail showing the money was legally imported should you want a visa in some provinces, or to buy a condo because you have to prove the origin.
Many people prefer to transfer via Wise or bank wire because there is less risk of robbery, theft or loss.
I would never be comfortable with a visa renewal scheme where I had to trust banks to reliably transfer ฿65k every month - so it’s ฿800k for me at 2.5% annual interest.