Are you after a T4 or a T5? Any T4’s are getting pretty long in the tooth now, early T5’s are not too expensive (I have a 54 plate T5).
I have the 104bhp 1.9TDi engine, you can get an 88hp version which I wouldn’t fancy, and more powerful versions that you don’t really need. SWB will fit in a standard car park space, LWB won’t, normal height roof will get in 95% of multi-storey carparks, mid/high roof won’t (and generally cost more on ferries, as does the LWB)
TBH, you just need to look for all the standard stuff – service history, belts changed at appropriate intervals etc. Cenral locking can go a bit squiffy, so keep an eye out for that, make sure it all works.
Are planning on leaving it as a van, or doing a camper conversion?