Just book the cheapest hostel you can find (under 500 baht) check in, ask for a copy of their TM30 filing. You are now up to date, go back to your Landlord and request new TM30, no fine.
Non O based on marriage. If you are remitting the proceeds of your business sale into Thailand make sure you do it while you are non tax resident otherwise you could get clobbered by the Thai taxman.
Legally yes, every time you change address. Enforcement however is patchy and dependent on your local immigration department interpretation of the law.