Pressure for the van tyres depends on type of tyres and the weight carried. The only way to find the weight is by using a weighbridge and measuring the weight carried by the wheels with the van loaded for the road. Tyre companies can then tell you the pressure you should run. I would like to ask about drive through sites. Having said that, it does give the van stability when you move around inside if the jockey takes some of the weight.
Some people even wind down the rear stabilisers for the same reason.
Personally I don't usually bother but it's a matter of how much movement you are comfortable with. Changing down when approaching a hill can be done with the throttle partially depressed with the aim being a smooth transition to the lower gear. If you have your foot flat when engaging the lower gear it will give too great a surge of revs and that's bad for the transmission train. I cause it to change by increasing the pressure on the throttle. If the hill is twisty I usually lock the transmission in a lower gear to prevent it 'hunting' up and down as you vary the throttle.