The earlier you take it out, the better off you are. I've had health insurance since I was 55 with no pre-existing conditions, so I can just keep renewing until 99 and everything will be covered. The problem is so many retirees in Bangkok go to extremes to avoid health insurance. Makes me ROFL
Takes 5-10 mins at immigration. You'll see the sign for re-entry permits. Hard to miss. After security, before immigration. 1200 baht. No forms or photos required. They do it all. Better option than going to the immigration office
In pre-covid days Thai Airways used to do transfer of luggage through Bangkok to CM and Phuket. You still had to clear immigration in Bangkok, but customs were cleared at final destination.. Probably not been reinstated yet