Don't remove the powder coat at all. It makes for an excellent surface for paint to adhere to as it's tough and durable and wont flake off in a hurry. Just give it a good rub to knock the shine off so your new coat has something to stick to.
As for the rings, if it's running fine and starts easy then leave it alone. Do the basic service items and put it to work. If and when it require a re ring, do it then, it ain't going anywhere. Most TAC's have do very little work compared to mowers, so if a 2 stroke can go 20 years on the same rings then your TAC should go 20 more.lol
On the subject of longevity, you stated earlier that you used a 40:1 fuel mix..... DON'T!! Use the correct 25:1 otherwise you could run the risk of damaging rings/piston etc.
