Here are a few just to give you an idea.
Rear wheels are 18X11 with offset of 45mm. 295/30/18's. I used a 4mm spacer straight into the adaptor which is 23mm from memory.
Front wheels are 18X8 with offset of 50mm with 225/40/18. Bolted straight onto the adaptor.
At the rear, the wheel and tyre barely fit inside the arch and I have it sat fairly low. I can't get my fingers between the tyre and arm so prob no more than 3mm clearance there and if you jack up the van (i.e. the suspension drops) then the inside of the wheel will catch on the spring tower.
You'd have to modify the spring tower in order for it to be safe for everyday use.
For what it's worth, I'd go no more than 10's. They will bolt on without body/suspension mods. I can just open my sliding door (with the 10's) without having extended the arm.
MG