Scott,
Sounds like the engine air compressor is working as advertized. My A3 builds pressure identically. As for the CTIS, start by reading all the attached threads Porky posted, lots of good info from others in the same boat (truck) you're in. Also good reference to the Tech Manuals you will need to maintain the unit. The Truck is safe to operate w/ the CTIS in the OFF position, it can wait. On the third day you own the truck, check it's vital fluids, all of them. Grease/lube the truck, lots of grease zerks to find. Obtain an Operators Manual and read it, lots of good, "I didn't know that", info. As Porky stated, park the truck after you have pulled forward and backed strait, keeps the tension/torque to a minimum on the rear axles. In a couple of months, you'll be the guy informing new owners on the ins and out of their new purchases. Good luck, have fun.
JC