First welcome to the club. Second buying a modded car can be risky. It says it has a Gruppe-S tranny find out if it's a RA gearset or what was actually done. The tranny would be my biggest fear, as a modded car usually indicates either abuse or hard driving. Unless you know the car or the seller I'd think long and hard before buying that.
Also the price is a tad bit high. I wouldnt pay anything over 17 for that car, mods will not help resale value and the seller should expect to eat most of their cost.