Every Bank branch can give you a statement for the last 6 months. Statements for 12 months they have to order from Bangkok Headquarters. However, many branches will refuse any service and gonna tell you to visit your home branch.
Border bounce with some agency in minivan is a kind of suizid. I recommend a flight to Phnom Penh, Vientiane or any other City in the neighborhood. That's not much more expensive and definitely not wasted money.
you leave only once. After first 60 days you go to your local immigration and there you get a 30 day extension. After that 90 days you do a border bounce or visit a neighbour country for a couple of days. Returning you get another 60 days and again a 30 day extension at local immigration.
You can't just change your address. You will always be connected to your "home branch" in Bangkok. After moving to HH I recommend to open a new account there.