people do extend. Or they might travel to other countries by land. Many reasons why you don’t need a return ticket. Thai immigration rarely ask if you are a first world country citizen.
First you need an address. Then you go to immigration and get a paper to open up an account. However they will need something that validates your address such as an affidavit from your consulate that will need to be legalized. Or if you are married to a Thai your spouse can help you with this. But realize without a letter from immigration or a yellow book the bank can not open an account for you. They really don’t care what kind of visa for you. They are more concerned about you having an official address in Thailand.
I opened up an account last year on a 90 day visa. More than likely you are not going to immigration to get a paper for opening up bank accounts, that gives the bank your official address.
I opened up Kasikorn account at a small store branch office in Khon Kaen with my wife doing all the talking. Deposited 1000 BHT with no issues. Had to provide a paper from immigration to certify my address and passport. I think the gal thought I was opening it up for a marriage visa. Anyhow the biggest problem was that she wanted to sign my name exactly the same on every document.
Yes. They saw my wife and I go to the foreigners line where it looked like a couple of hundred were waiting and we got escorted to Thai line where only two were waiting. And we got a lot of „How come he gets to go in that line“