There is actually no fee to open a bank account, but most banks will require a initial deposit of 500 baht to open you a account. If they are asking a fee, or are trying to sell you insurance, walk out and try another branch or another bank.
I have had the same TM30 for the last 6 years now, as I live in our house, your TM30 will be valid, until you change addresses, or returning from a overseas holiday, some offices will require you to lodge another TM30 upon return to Thailand, even if you are returning to the same address.
You also might require a completed TM47 form in blue ink, a lot of offices ask for it now. Plus your passport, a up to date TM 30 and you should be fine.
You never can tell, I have had it checked before at check in, and sometimes no. Always depends on the individual checking you in, but the rules are the rules so don’t go over your allowance.