As it happens, i fix a lot of these as they are imported from germany then sold on to spanish, after metriculation to spanish plates including itv test etc!!!
If it is the 2.5tdi, you will be impressed with performance,keep oof the loud pedal and the consumtion for such a big van is very good, as said belts are a pain, and the injection pump belt can only be set up by computer or good dti gauge, but there is a lot of faffing around to do on it to get it right, it will run when you close enoiugh but the economy stinks and the power is down till you get it smack on!!! DMF can give trouble and is a pain in the arse to do, obviuosly do the clutch at the same time, drive shaft cv can get noisy after high miles so check these carefully although a pretty easy job to sort due to the design,
check the rubbers carefully as they split and get left,
sliding doors ALWAYS have dents in them!!! intercoolers can rot through so check, carefully, oil and filters are a must very regularly, front steps can rot easily fronmt shocks can wear owing to the weight of the front end, very often find rear calipers sticky as they dont get much work when its empty, brake fluid is very rarely clean as no one changes it,
abs can sometimes give trouble if its fitted, with warning lights coming on when they feel like it, usually sensor probs
thats about it that i can think of at the moment :-/ and of coourse this is only the mechanical side, body and interior you should you think of anything ask?