hi, the 98 gt tdi has a 110 bhp engine, probably a AHF engine code
i had a 6 disc boot changer and sunroof with mine (but i dont know what was standard really)
A 5 speed 'box,
what to look for?? well .....best to check in the "common problems " page in the mk4 section really, it ranges from window clips to the faulty MAF sensors... worn rear axle bushes make the rear sound loud and bumpy on pot holes, but a relatively easy repair
just make sure the cam belt has been changed and that its had regular servicing