some embassies ask for 3 or 6 months worth of statements but the balance can fluctuate as long as the final balance is over 500k Best to check either your specific embassy
not technically but to get the 12 month extension based on retirement you need 800 K THB in a Thai bank for 2 months prior to applying for the extension and 3 months after with the balance not dropping below 400K
I am sure this is explained more fully on the official visa website
Every medical DTV I have read about required meeting the medical practitioner in person and getting a treatment plan
Some people managed approval based on 1 appointment but that is unlikely now but even those were initially in Thailand to get all the paperwork etc and then applied from outside Thailand