I'm running something similar to what you want with a Dispatch Combi swb. 6 seats (in 2 rows), bulkhead, 4 x full size bikes (front wheels out) on a shelf 2/3 depth of the boot, extra tie-downs etc. Huge tailgate is ace as a shelter.
Insurance happy bulkhead / bike carrier improved safety and wasn't classed as modified as it bolts into existing mounting points. Not a bad van, 1.6 is slow and still fairly pricy to tax - I imagine 2.0 will be even more expensive on tax. I think you'll find it very slow compared to S Max. Could probably be much improved with a remap - the power and torque curves are very flattened compared to other versions of the 1.6 HDI (I guess to protect the gearbox if towing fully laden).
Same vehicle available from Peugeot, Fiat and now Toyota. If haggling second hand, worth knowing that the new purchase price was almost certainly 20-25% below list.
The only off the shelf option I found was a Transit Connect (they do a clever sliding steel mesh bulkhead that goes behind the rear seats and pushes forward on tracks if you fold seat up). However Connect maybe not be enough space for you, and not sure what Crew van / Tourneo come registered as on the V5 (but I guess could be changed to dual purpose vehicle to get car speed limits).
Doublecabin is a very solid conversion but pricy (£2k). http://doublecabin.co.uk/