DTV requires 500k baht in savings around 12k USD but you also have to demonstrate reason like remote working medical treatment or classes you can apply for 1 yr tourist visa with multiple or one entry
I would keep them on you just incase I seen of two people denied cause they didnt have the required funds for the DTV so id make sure you have that in savings
It depends on how much you bring in they have tax brackets, but it will also depend on personal situation for example. I will never pay taxes on my income from the US due to a treaty signed between the US and Thai government DTA, thailand will not tax entitlements/ benifits that are paid out by the Federal Government such as retirement / Pension at the federal level or Compensation such as VA disability
Yes, you have to be out of the country to process once approved leave thailand with the dtv letter come back in show it to immigration and you get a DTV stamp. Can be same day most goto Vietnam and come back