I have a 98 VR6 Auto twin slider. Currently Mileage is 167K
I bought van just over 2 years ago at about 162k, no real service history, about 8 former keepers, but stamps in the service book from private garages. When I got it it had 2 dodgy injectors that would have worked out a fair few quid for a garage to fix, I got some 90k mileage ones on ebay and they are good as gold.
The engine is the old 12valve VR6 - 140bhp up until about 2000 - Its thirsty, but fun

. Fuel economy averages at about 20mpg ( I do drive pretty hard), equally on a long run cruising at 60 on the motorway I have had it as high as 28mpg. I have some slight rattle/tap from the engine, but its high mileage so not really surprised. Because of the dodgy injectors, when I got it the thing didnt change gear properly, it would jump between gears and made me think hmmm, even after I repaired the injectors and the engine was pretty sweet, however, doing a throttle adaptation procedure with my laptop connected, followed by clearing the fault codes means it changes smooth as silk!
Caravelles are great as they tend to have better specs, mines got heating in the back, electric windows, AC and an electric sunroof.
Watch out for ones with sunroofs, they arent like the cars and rely on a seal to keep the water out, mine is about 95% so if I park down hill occasionally water can get in.
I specifically bought mine for moving house, it has done an amazing job, the autobox makes it lovely and lazy to drive too.
I'd say your biggest friend will be plugging a laptop in to find out any fault codes. The autobox is fine, as mentioned as long as its been serviced. 100k is pretty low mileage for a T4, I have had good and bad experiences with high/low mileage vehicles, I had a V5 bora with 82K about 4 years ago, I dont think it was cared for properly, early service stamps in the book were not all VW, struck me as a rep/rental car or something, it was fine but you could tell it hadnt been loved as much until one of the last owners, just bought a golf mk4 (VR6 4motion!) with 72K on the clock, no receipts, but stamped up to date, yet the amount of things I am finding to repair on it is quite surprising for just 72k, like rear wheel bearings, trim parts etc, even though its practically not been anywhere. My caravelle at 162k I have done the injectors, CV gator, just replaced an exhaust section, age/mileage stuff you'd expect
I suppose the big question is what are your mechanical skills like.