If your going to buy an oldish van try and check it out as much as you can, get a mechanic if you can. I started up a exactly a year ago, bought a Citroen Berlingo for £1000, i had it 9 months and head gasket blew, in total id spent £3000 on the van and that didnt include getting the head gasket fixed. In the end ive got a new Nissan Primastar but at a cost on finance.
Its a difficult desision, buying a van outright means you obviously dont have any outgoings, which is good for 1st few months until you pick up more work, but it can go wrong at any point.
Although it cost me £3000 in 9 months I couldnt afford a new van when I first started so although its a lot it did work out better for me.
So all i can say is take you time looking for a van, dont rush as i did.
Mark