Perko G Rose. You get only 1x90 days, cannot be extended, and if you leave the country in that 90 days, the visa is cancelled and you cannot re-enter on it
Forget the STV, it's coming to an end. Go for a multi-entry tourist visa and with extensions and two strategic border bounces you can get almost nine months from the one visa
Every bank branch has a different policy on this. My advice is to join a Chiang Mai expats group and ask the question there, as those group members would know which bank/branch specifically would be the best to approach