If you live in Isan, why are you opening the account in Pattaya? Many banks charge an ATM fee for use outside of the province the account was open and there are certain things that you can only do at the branch the account was opened at.
You can file a TM30 yourself at Chiang Mai Immigration - need a copy of his tabien baan, lease/rental agreement and a form. If the address is already on file, only the rental agreement and form. Source - I've done both ways before.
You can't apply for a tourist visa within Thailand - you need to go to a neighboring country or back to China to apply through an embassy or consulate. There's also no three-month visa for a tourist - different if applying for a retirement or other type of visa. There is a 60-day single entry tourist visa that can be extended for 30 days at Immigration.