I rent a studio in a great building no contract just month to month for $300. I rent a small scooter $80 a month. Unlimited data and calls mobile package around $15 a month, wi fi is free in my building. Eating out Thai food/ street food around $ 12 a day but depends on what you prefer if you want western food or enjoy nice restaurants then its going to be more. I think you're way over on most of your budget but I live pretty cheaply. Main costs are booze and women 😆. I've lived here 4 years so any questions just ask.
Yes you can. Residence certificate needed. Go to Land Transport Office or satellite ask for relevant paperwork ahead of time, just makes things easier. Copy sellers ID and green book.
Looking at your stamp, you have to leave every 90 days. So I'm guessing you have an evisa of some kind.This is probably the difficulty you are having. I opened a bank account on this visa last year at Bangkok Bank in Pattaya.