Didn't you know that? You pay millions and millions of baht for a 20-year elite visa and then only get six months because your passport expires in six months 🎉🥳🤗😜
The immigration officer would certainly give you this answer if you showed up at his counter without a digital arrival card. I doubt you'll have to pay a huge fine or they'll send you back to your home country, they'll just tell you and then you'll just do it.
Theoretically, it's possible, but it's not enough to just walk into the first bank you see and think you'll get an account there. You'll probably have to walk into 30, 40, or 50 banks and try consistently. I'm sure then you'll get a bank account. There are a few success stories, and as far as I can remember, they included among other things a certificate of residence. I would collect everything from Thai driver's licenses to your health insurance. They just want to see as many official documents as possible to make sure you are legal