i am looking for an answer to the question: during my first year under a non-O retirement visa, can I withdraw 400k THB from my bank account and keep a balance above 400k THB until 2 month before my visa extension or do I have to keep a balance of 800k THB at all time? I am in my first 12 month living it Thailand.
Depends what country you are from, what fiscal agreement it has with Thailand. It also depends on where the money comes from. If comes from Thailand, taxes in Thailand up to 30% depending your bracket. If from other country, find out what are the fiscal agreements.