All bank accounts now need a registered phone number that the phone company has linked to the same name as the account holder. If your bank hasn’t asked for this yet they will.
Not a requirement for the visa but an extension will only be granted up until the validity of the passport expiry date, so if it expires in 8 months for example you’d only get 8 months from a year extension.
Thailand doesn’t actually have a limit of how long your passport is valid for but airlines almost certainly won’t let you board if you have less than 6 months left on a passport.
You don’t get a “visa on arrival” with a US passport. With no visa you’d get a visa exempt entry stamp for 60 days. You can extend that once for a further 30 days.
To get longer then it would be advisable to use a “border bounce” company that facilitates such. They know the wheels to grease and will get you back in.