Immigration on DMK won't give you a transit visa. If you aren't allowed to enter on visa exempt, you need a TR. Better book an airline through BKK Airport.
never heard of such kind of account, but in that case you need to open a new one. It's with non-o visa no problem and done within 15 minutes at any bank. I recommend Bangkok Bank or Kasikorn. Anyway, even with a new account you need to activate these functions at the ATM.
Ask at your branch to activate the online banking and the online shopping function. It's not active automatically. Afterwards you will be able to use the app as well as the web online-banking and your debit card.