What are the requirements for maintaining a retirement visa in Chiang Mai after returning from abroad?

Hopefully you have not ALLOWED the Thai bank account balance to fall below 400,000 during the current extension year.

1) in Chaing Mai, yes. there were reports they were required to submit TM30 after coming back from abroad to the same address.

2) If you want to travel outside Thailand, you must have a valid re-entry permit before you leave. If you don't have a plan to go out of Thailand until your current extension finishes, you don't need a re-entry permit.

3) In Chiang Mai, they accept your next 1-year extension application when you have 45 days or less with your current extension. You need to have your full funds of 800,000 THB in your bank for 2 months as of the application date. And you need to keep it until three months pass after your new extension starts.

Here is general information for retirement extension. Get a handout (or photocopy) of the latest requirements at CM before you go really apply for your next 1-year extension.