I'll try my hand a few answers
I haven't looked at an A-trim kit, so it would help to know what's included. Let's assume it has at least a fuel management unit.
1) the fuel management unit (if included) will restrict the return flow of the fuel to the tank under boost. This will make the 19lb injectors perform like larger injectors up to a point. If you have a standard Mustang type of gas tank, I'd up the in-tank fuel pump to a 255lph unit. This will meet your immediate needs.
2) all 5.0 motors and tune-ups are different. Only a dyno will let you know for sure.
3) you will feel the difference.
4) if your configuration is the same as a stock 89-93 5.0, it should be relatively easy. The bracketry will relocate the alternator and smog pump (if you have one) to allow fitment of the supercharger head unit. You will need to have access to fuel line disconnect tool if you are running stock type rails and fuel lines to install the fuel management unit. You will have to punch a hole into your oil pan for the blower lubrication, unless you use a standalone oiling system. Whatever you do, take your time.
5) I don't see why not. If you get into additional work, such as non-stock cam, bigger throttle body and mass air, you will experience the joys of trying to tune it like most of us have already been through :D
6) I went high 10's at 128 on a 98,000 junkyard motor with an S-trim. Stock roller motors are pretty tough.
7) the blower won't be as loud as a you think. Just a nice whine.
8) the boost level is relative to the amount of restriction you have on the intake side of the motor. You may very well see 6psi. Double check on the www.vortecheng.com site, but I believe the A-trim is upgradeable to a standard S-trim. I've been wrong before.
Good Luck!