The goal of that banked money is to be a reserve for expenses (medical, emergency travel, family emergency). If the banks block the funds, what's the point of having it at all. Get hit by a bus and can't pay the medical expenses because the bank has a hold on your funds?
Passport, tm-30, passport photo. Residency certificate are type specific so your need separate ones for banking, drivers license(s), vehicle purchase/transfer/registration. RC's are valid for 30 days. I take along my lease agreement too.
Depends on your country and their DTA with Thailand. Depends on the source of the money. Depends on if you've been in Thailand for more than 180 days in a calendar year. So the answer is "it depends". Giving more complete info will get a more definitive answer.
you don't understand the difference between tax residency and tax liability. You never lose your liability for taxes in USA even if you are a tax resident in one or more other countries. You are wrong.