Had 2 TD5's, a GS7 and a Landmark (now on D3), both 60k miles in 2 years on each. Only real problem was a leaking rad on the first one, replaced under warrenty. No major things to look out for, other than a couple of well documented issues, these being:
very early ones had some issues with flywheel, buy should have all been sorted under warrenty.
And oil leaking into the injector harness, and ultimately into the ECU, but again, if your buying a later one, should be sorted.
Dont get too hung up on getting ACE, as a D2 corners/rides much better than a D1 due to wider wheel track. Get one with Climate control/air con. All 7 seaters have rear air suspension, and do give a strange feeling when towing (but a great tow car by the way).
Good luck - go for it.
Al