Just unnecessary additional info as many people are mixing up visa validity and entry stamp.
As Lloyd said, the visa itself's validity of 90 days (<- the period you can use that visa to enter Thailand to get an entry stamp for the status on the visa) starts on the issued date but the Thai embassy/consulate.
Your 90-day stay on Non-O starts on the day you enter Thailand within the visa validity as day 1, even if you enter Thailand on the last day of visa validity.
CW office accepts bank letters up to 7 days old (including the issued date). Get the letter and transaction in advance.
You can update your bankbook anytime on the day after midnight. You can deposit/withdraw and update your bankbook on ATM/CDM/PUMs before the branch opens.
There are copy shops one floor under and they are open before 8:30.
Yes, a 90-day report can be done by your wife with your original passport and required documents at your local immigration office. No problem. No POA is required.
Q. If I arrive on a Non Imm O single entry 90 day visa, can I fly out and back again within the validity period of the visa (with a reentry permit)
-> Partially yes, you can leave Thailand and back again with a valid re-entry permit within the period of the first entry stamp you already have, even after the initial visa validity.
Q. and be stamped in for another 90 days?
Not another 90 days. You will be stamped until the same date with the one on the first entry stamp. A re-entry permit can keep the current stamp alive, but cannot add any more days to that.
Funds of 800K baht in a Thai bank account are required for each applicant for a visa/extension based on retirement. In case one of a married foreign couple is applying for an extension based on a dependent on a retirement visa/extension holder, the applicant for dependent is not required to have 800K baht.