Do the full costings before you decide to buy second hand against leasing/contract hire.
I know that you are setting up on your own, and will want to keep your overheads down, but it can work out cheaper to have a new van on a lease. Its not hard to get through a couple of grand a year on MOT, repairs, missed work etc if you pick a bad 'un.
We run mostly new vans on contract hire - not because we are rich, but because experience has taught us that its generally the cheapest option overall. The only time we run vans older than 3 years is when we have had the van for the first 3 years on a contract and know its history - then we might buy it from the contract hire company, particularly if we have dented the bodywork (which is really expensive when you hand it back).
It might be worth using £1k of the money you were going to spend on a 2nd hand van as the deposit, and putting the rest away against the possibility of having a quiet month - you will have a few months of van payments sitting in the bank.