So back to back and overstays and you wonder what to do? You have already labeled yourself. You might get lucky and not get blacklisted. Go back to Vietnam and buy a legit visa.
Using the express immigration lane at Suvarnhumi makes things a breeze the immigration offices know you have money so you'll be spending up = good touist
My reason for saying it is the amount of road fatalities relating to buses of all sizes in Thailand. Did a visa bus ride 9 years ago before I knew better and barely slept through the fear of the speeds we were doing.
Couldn't pay me enough to get on one of those buses. Did you really get a tourist visa at the airport or a visa exemption stamp? Either way you can extend both.