You would really need to know the "sprung" weight on each corner. I don't know why folks always post total rig weights in threads like these. You need to know the weight minus the wheels, tires, axles, etc.
With the Fox shocks the N2 pressure sets your spring rate and ride height at the same time. The amount of oil will "trim" this in somewhat due to the change in cylinder volume. The amount of oil you put in them really depends on how you valve it and how much shaft is showing at ride height.
I recommend towing the rig to a scale and getting the F/R weights, then do some research on the unsprung parts to subtract those weights out. Once you have those you can start figuring it out.
Otherwise, test and tune...
There was a long thread on Pirate for the ORI struts, I bet there is one for Fox Air Shocks. I have 2.0s on the rear of mine for load assist with my leaves and a set of ORIs on the front. I just play with them to figure out what works, because no one else has a rig like mine so there really isn't someone to copy.
