I agree that this is unique to US citizens and seems absurd in your situation but look at the flip side. You have calculated, after all these years, that there is value to keeping US citizenship for you and your children.
They do tax 85% of our Social Security. When SS was running out of money in the early 1980’s the fixed the problem by gradually raising the full retirement age from 65 to 67 and they started taxing 85% of the benefits. Social Security is running out of money again so they are thinking about how to fix it again.
I’m not sure what the comment means either but we have to report whether we had more than $10,000 in a foreign bank account each tax year. It a simple form each year. We can’t hide our money.
I think you just have to file a final return with the IRS to pay any outstanding taxes. Other than that the fee to renounce is $2,350 plus any lawyer fees you may incur.
You need a second passport to renounce your US citizenship. Getting citizenship in Thailand is pretty difficult. Before you worry about paying taxes in Thailand vs the US you should worry about your next passport.
Your friend is wrong about other visas. I my 10 year LTR visa is multiple entry. I don't need re-entry permits. You just have to know the parameters of your visa.
If you need to get a one year statement from your bank then find out how long it takes. Some provide it same day. Others may take up to a week. This will effect your timing to go to immigration.