Never heard that with an METV, I mean that's the whole point of the visa, that you can enter Thailand multiple times! I think you're confusing this visa with SETV's and visa exempt entries
That'll be the old way. The new evisa system doesnt require mailing in your passport. You get the visa via email and print it off to show Immigration on arrival
The norm for Non Imm O applications IS same day approval if all your paperwork is in order. There's no seasoning of funds required for the initial visa.