Welcome to the forums!
Good to hear to you decided to join. Sounds like you've been hard at work fixing the previous owners negligence. Should last you virtually forever now though
I wish I could help you out with your question in regards to the burnt piston ring. It's never happened to me so I'm not sure what tell-tale signs to look out for on the piston itself. All I know is that if the piston rings are shot, the car should smoke a fair bit and use excessive amounts of oil. A compression test would be the best way to diagnose it, but you could always make a thread in the Camry forum and hopefully someone will know of quicker way to determine if it's the rings at fault
Best of luck, and once more, welcome aboard