The Mountain Kat

I picked up a nice low mileage set of Callaway-Eibach coilovers locally. Someone had Callaway set their car up and then didn't like the ride. I like the feel, handling, and for the most part, the ride. I want to try running just the coilovers and I called Eibach and asked one of the engineers a few questions. None of which was answered. First is that these are some 5 years old so would it be a good idea to change the fluid and if so what with. Second is that I want to check the pressure. What should it be and what do I use if they need "air"? Discount Tire can pressurize them with Nitrogen. Which if I remember correctly is the preferred gas for shocks. Thirdly is what spring-rates would I need to use on the coilovers if I want to be close to it a little stiffer than a ZO6?
All that I heard from the Eibach engineer was that the coilovers won't stand 800# springs. Fine but I figured that much from the aluminum housings.
Does anyone here have the answers for me?