As long as they give you a receipt or a screenshot that they filed the TM30, you're fine. Hotels normally use the the online TM30 system, but it doesn't always work. Ask the for a screenshot.
Vit is correct. When you transition from a visa exempt entry to a Non-O based on retirement you'll get a 90 day visa. The 800k baht does not need to be in your Thai bank account for any period of time.
After the 90 days (well 15-30 days before it expires) you'll apply for a 1 year extension. The yearly extension requires the 800k baht to be I'm a Thai bank for 60 days prior to the application.