5 years or 120k whichever comes first I think for Cambelt. Definitely make sure service history is good. And oil changes for gearbox and quattro system. Check out buyers guides on YouTube
I did it for peace of mind. Regular oil changes/flushes etc.
I was doing minimum once a year. More if I were doing road trips.
Got to get my engine rebuilt now.
I'd recommend you look at getting a stainless steel straight through exhaust. Powerflow are reasonable and I know people who have used them and been pleased with the results