Please realize you'll not only have to attend but also make progress?
Are you aware you'll also be interviewed in Thai by the immigration officers to confirm such proficiency progress each quarter, as they review your request to extend?
Finally, most "good" schools are booked up for the intro/basic levels already.
The top three schools in Bangkok listed here in alphabetical order.
Look into ALA, Duke, and Rak Thai schools.
YouTube background music is for extraneous entertainment
It'll be best for you to open any account near where you live, that'll be to your advantage because all banks are fussy about doing simple things (such as change of address, update any information) at the branch where the account was opened.
Bangkok Bank in EmQuartier next to Phrom Pong BTS SkyTrain station may still allow you to open an account by yourself; stop by with your passport & see their list of requirements.
Besides that:
Siam Legal, a law firm will sort you for a fee. Might be 5k thb