I have Immigration's 'Receipt of Notification' and if you're saying that is sufficient thanks for your help. When you say 'Other Requirements', I assume you don't mean financial criteria as I presume they are standard throughout Thailand?
My address has been reported in person every time I entered the country by visiting immigration with blue house book and Thai ID. Is this the same procedure for an initial retirement visa application?
I live in Kanchanaburi and have used the Phu Nam Ron (Kanchanaburi) crossing many times without any problem. You leave your car 100m before the border and walk to Imm. For a Non-Imm O the only cost is 960 baht paid after you have passed through Imm. at a window on the LH side. For this one-off payment you are ferried by van to Myanmar, the driver does all the paperwork, you sit in the van. He then returns you and in/out stamped passport to Thai Imm - very straightforward. I've never been asked to show 20k.
On a Non-Imm O for a UK pensioner, I flew from LHR on BA last week using the second half of my return ticket originating in BKK and was not asked for confirmation of onward travel nor have I ever been. I always presumed the reason being that the visa is 12 + 3 months and therefore the possible final departure is outside the lead time for purchasing airline tickets. At BKK the IO was a few minutes flicking through my compilation over several years of Non-Imms and Retirement stamps before asking how long I wanted to stay, my response 90 days. No mention of 20K. While standing in the queue I did notice the adjacent IO was processing arrivals at twice the speed.