Not true. Ekectronic payments are not equal to electronic banking.
You are confused.
It's like a petrol card.... you give access to nothong more than the pre-advised funds nothing more nothing less. Needless to say these cards are not linked to the main accounts but hold only pre-advised funds
You can fly trough domestic from cnx to bkk. Then after your hotel visit in bkk city you can check in international in bkk.
If you check in international in cnx you have to stay within the transit zone in bkk. There is a hotel inside the transit zone however but its rather expensive.
That's plenty of time but I suggest you take a motorbike-taxi to the border from the bus station instead of a Songtaew.
Also when you enter the Myanmar side you just tell the immigration officers "no shopping" and they will stamp you right in and out the same time. Turnaround at both borders should take no more than 30 minutes so you have time to grab some lunch as well at the busstation.