Hi Multivan,
I have a Transporter TDI so the mechanics are the same. I get about 30 MPG (Imperial galls) around town and 33 on a run. It's said that 43 is possible. The service history is very important so check the service records carefully. The timing belts(2 of them) in my book are listed to be changed at 80,000 miles. My advice is to get them changed sraight away if they haven't already been done.
The engine on these being 5 cyl should sound unusually smooth and quiet for a diesel with almost no smoking at all and no metalic tapping. The gearbox should be quiet too. Make sure there is plenty of life left on the clutch as it is a major job on these, involving repositioning the engine with a special tool while the geabox is being taken out.
The multivan is a great vehicle, you'll love the handling with independant suspension all round, the engine is superb with 102 bhp on tap, and the all round disc brakes are really powerful. I'd like electric windows though as I'm fed up with the ridiculous 11 or 12 turns from closed to open!
Enjoy your Multivan and remember to post pics in the members gallery!