The fact that you don't need a TM30 for a re-entry permit at the airport is probably due to the fact that you are in the process of leaving so your residence in Thailand has ceased/been suspended
The deposits must be while on a long stay visa or extensionso you can start on the Non-O. If you start after the extension is granted you may only have 11 deposits when it's time to do the next application.
start the 65k deposits before the first 12 month extension is inked in as 12 monthly deposits are needed at the time of the second application which can be 45 days before the first extension expires