RE: what sould i know about 88 90 quattro
At that high of mileage, you should look for a good engine supplier! I say that hoping you won't need one. These are well engineered vehicles... run a carfax, obviously.
As far as maintenance schedules, you can get those from the dealership. I would definately have your timing checked. I think there is a timing chain on your bad boy; if it's a belt change it.