I don't know...
Mine is a '92 Cargo van with the 5.7 liter V8. I bought it with 68,000 miles on it, and it was in pretty good shape, except the interior was an old custom job with shelving in the back (was used for an interior decorator's sample hauler or some such).
The only thing it needed was a $13 part for the A/C controls, because the vacuum switch was leaking.
I paid $2300 for it about 3 years ago, and I'd buy it again over and over.
The only thing I can think of off the top of my head as a common issue on these vans is door hinge pin failure.
I've seen a lot of vans running around with bent edges on the fender and door from where the door sagged and caught the fender.
This is obviously not an issue on the van you're looking at, but I'm just trying to brainstorm.
I'm sure there are probably other things, but I can't think of any right now.
Accessing the engine is not so much difficult as it is different. Some stuff you can reach from under the hood, but other stuff has to be reached from under the dog-house, which can be a minor pain because you have to remove the "center console" for lack of a better term and the engine cover itself (dog-house), and the seats are kind of in the way.
However, it is much, much easier than working on my '85 Toyota MR-2 or my '96 Camaro. LOL
As far as parts availability goes...
Most of the mechanical stuff is easy to get, and is relatively cheap, with body and trim stuff being a little more difficult to source, and replacement conversion specific parts being the hardest.
When I'm considering buying a vehicle I'm not familiar with, I usually go to an auto parts store's website and look up parts that I'm likely to replace (brakes, filters, etc..), and see if there's anything that throws a red flag (Like my BMW X5's $300 battery (Don't worry... I sold that headache)). Our vans don't really have that, as most of the things you'll be buying regularly were shared across several other models, so the parts stores usually have regular maintenance stuff in stock all the time.
Frscke1's advice is sound, and in my opinion, if it's not rusty, hasn't been wrecked, and will pass whatever inspection your state requires, I don't think you'd be buying anything to be intimidated by. The thing that intimidates me the most is a possible fuel pump failure, as you have to drop the tank to replace it, and that can be a pain. A heater core failure can also be a pain because you have to pull the whole dash out to replace it (I did mine a year or so ago), but the part is only about $20.
If you're coming from the Subaru and Mazda world... You're probably going to think the van parts are free in comparison. LOL
I have no idea what the roof rail capacity is, so I've got nothing there.