Bob,
You should call Pure Flow Tech. at 877-463-4373 and ask for their tech. person, if he isn't in he will call you back promptly, at least that has been my experience with them. I've had my AirDog FP-80 on for a little more than 2 years. I can answer some of you questions from my experience and from what I gathered from Pure- Flow's tech.
A) It is my understanding that the FP-80 and the FP-100 are the same unit.
B) There is no difference just a name for the later built unit.
C) Same installation since they are the same units.
D) They are supposed to be set to deliver 15 psi at idle.
E) Yes, the pressure can be adjusted: You can pull the fitting on the return line going back to the tank and there is a spring and rubberized check ball there, You can call Pureflow and get a stiffer spring, or you can stack 1/4" washers between the spring and return fitting until you get the desired idle pressure.
F) I also ran through the OEM filter housing since I already had a Vulcan big line kit and I also wanted to retain the fuel heater and water in fuel light. When I first installed the AirDog running through a new OEM fuel filter, I was seeing 13 to 14 psi idle, 12 psi. cruising, and no less than 10 psi. WFO. Pure-Flow's tech said I was losing a little flow through the OEM canister. He gave me the suggestions I gave you in E and I chose to stack some washers under the return spring. I ended up with 2 thin 1/4" washers which gave me a solid 15 psi at idle, 13 to 14 psi cruising, and no lower than 12 psi. WFO.
G) I haven't tried this so I can't comment on this.
I also see the original owner, Charles Ekstam, is back in charge of Pure Flow, which if you haven't followed things, the owner of Fass, Brad Ekstam, is his son and they worked together until there was a riff in the relation ship. The original units were called Fuel Preporators and they were for large diesel trucks. That's why you see similarities between Fass and the AirDog. I chose the AirDog because it was compact and protected up above my transfer case skid plate on my 4x4 and I have been very happy with the unit. I hope this helps.
Regards, Mike.