Hi
I would reduce the number of twinsets unless you are determined not to buy any trimix from the boat. 1 twinset, 1 deco bottle and 1 stage should be enough per person. Keep filling the stage, either with trimix for the morning dives or 32% for the afternoon dives. From the plan you describe I would think you should only need 3 12L fills of Trimix onboard.
The transit van should take it all. The one I hired last year had only 8 twinsets and 12 deco bottles. However, it did have 8 people aswell. It will take 14 hours to get there from London as the max safe speed is 60-65mph, some new ones are limited to 60mph. Unfortunatly, as I organised a trip last year I had to delegate the driving of the van and had to drive an automatic, air conditioned Audi
It only took 10 hours.
jd