as you already have the pump and tank you will need something to make pure water, fit a di vessel in the back of van, if you are considering doing domestic window cleaning too then you would be better of in the long run with a ro as it works out cheaper,
as for the pole and brush again depending on what you wanna do, cons = short pole........ windows = long pole
a booster pump is not always needed, ie if your tap water has good pressure to your ro unit then not needed, if low pressure then b/pump is better
hose reel........ if only cons = short length,
if windows = 100 mtrs micro bore is best
hope this helps
jay