Welcome on board Dean!
Good advice above. For the money you'll get a good car.
Camebelt/Waterpump needs changing every 4 years or 60k miles (whichever comes first), costs £400+ from a VW garage, worth remembering if you buy a 7 1/2 year o,d car.
Things peeps change (and/or update) for peace of mind are the Diverter valve (£35), PCV (£35), cam follower (£30). The engine is pretty bullet proof on the whole.
Rust on the front wings is something to look for on early GTI's, even if you find a car with this, its no biggy as VW should sort it FOC.