Ok. It didn't work for me, so the OP can take a chance on what you say. It's their choice. It's just as easy for me to order 12 months statement from my local branch, which takes five days and 100 baht and I know 100% it will be accepted. I wouldn't take the chance just to save 100baht - but as I always say, each to their own
You're better off building up your nest egg in your home country earning a slightly better interest rate (not much admittedly but everything adds up) and when you're ready for the visa transfer the 800k lump sum in one hit.
On the Thai side it's Aranyaprathet. It's probably the worst land border to attempt a bounce. You could well be sent to Siam Reap to get a flight back.
Absolutely that's an option, and you still have the TR visa up your sleeve if you want to stay even longer. So you could in effect get five months stay, with just one border bounce. And you wouldn't be questioned at all
You can only try. If absolutely worse comes to worse just enter on 30-day visa exempt, then at the end of the 30, do a border bounce and activate the TR when you re-enter