My 91' won't even think about lifting on 100 PSI in the tank. It isn't enough to untuck the tires but my truck lays frame & is bodydropped so I have a lot more to go up to get ground clearance... I have never put a guage to the bags to determine my rideheight. I put it where it feels good, then check the psi, from there go to a GOOD alignment shop & have your alignment done. Schrader valves are good to have as a backup incase of compressor failure or other issues...You will want them installed between the valve & the bag(as close to the bag as possible with a ballvalve installed between the valve & the schrader valve to hold pressure in the line incase your failure is a stuck dump valve or a blown airline).
You would want a compressor capable of 175 psi output but you should be fine if you run a 150 psi pressure switch. I would reccommend a Viairr 450 compressor. They are 100 % duty cycle, meaning they can run all day if needed w/o overheating. This is one area where I wouldn't skimp. If your compressor craps on you, how are you gonna lift your truck up to get it home from a show??? Remember, buy good quality components and you will have a reliable system.
As far as the Harrison A/C compressor is concerned, yea you could use it but I don't reccommend it. If you want fast air & a lot of it, use a York 210 A/C compressor as found on the late 70's to early 80's Jeep Grand Cherokee's, AMC's, F*rd cars/trucks/vans. The Harrison compressor rely's on it's lubrication being circulated inline with the refridgerant. Since you are not running a closed system, you will need to have a constant supply of oil for the compressor with an inline oiler. The York model compressors are the ONLY one's that have a built in oil sump and are lubed much like a Briggs & Stratton by splash oiling. You will still have to add oil to the York occasionally but they are 100x's more reliable than any other compressor.
Using the 3/8 valves & 1/2 line will be a nice system. You don't specify what size ports you are running on the bags themselves but I assume 3/8"... you will be happy with it...
BTW - I always use 2600's all the way around on any truck I bag. S10, Fullsize, import truck... They give a nicer ride than a 2500 IMO and a tad more lift...