OK Tosh - that pic you posted is the baby.
The 815kg payload jobby is fine for you, 500L a backpack and worlass. (After all she is only about 50kg
of gorgeous fitness errr ... and very slim and athletic, tops.
)
I know several windies who use these vans with 2 up and a 400/500/650L tank. The 650 husband and wife team I know drew a line on the tank at about 550L so as to not go over the 815Kg payload. I went to the Dursley auctions this time last year with one windy and there were several vans and he got a nice 06 on 38000 miles for £3.8K - he's got a 500L on board and another I know has a 400 and takes 2 or 3 25L barrels for his backpack which he uses too.
The greatest window cleaner of all (My hero - Roy Harding from Monmouth) has one (or the Citroen equiv. - same van different badge) and I bet he'd let you see his - his was new I think - on a 2003 plate.
Don't go long wheelbase - don't go to the new shape - they are less easy to park and get onto narrow drives - completely unnecessary IMO. But don't get a 1.9 - get the 2.0 110bhp diesel - they are more powerful and economic. (I've got the same engine in my Pug family estate and it's on 170K and drives like a good un.
These vans project the right image of being serious about your business without being "vanwrap overkill lookatme and my wedge".