you don’t actually have to file in all cases. Very much depends on the individual situation. Only money that is “assessable” is subject to filing. Its not straight forward, depends on type (source) of money brought in, and details in individual tax treaties
lol, are you high? Its the total number of days obviously. And DTV can be extended. But even if you exit and come back, tax days will not reset lol. Its the total number of days you spend in Thailand…
Exchange shops are usually cheaper if you choose the right ones, superrich or Vasu of in Bangkok. Though they are quite picky with notes. Slightest damage gets rejected.
But many exchange shops have horrid rates as well, so do your research based on your location. And avoid exchange more than absolutely necessary at airports.