If it is a DD the only weight reduction i would do is spare, jack, everything out of trunk, RSD, and tubular K-member. You can remove amps and stuff and replace all with a generic stereo. For a DD anything else will get annoying.
get the mongoose, install it, put it on a dyno to check the A/F. You can fax them your graph and info and they can adjust your chip if needed. They are easy to work with and will do what it takes to make your car perfect. The tunes are usually right on.
I have Baer brakes all around and they don't rust. But the center section will get oxidized and get a light concrete color to them. It is not that big of a deal since I have silver rims, all sort of blends in.
If your rotors got turned down then you will need to re-season them, and anytime you get new pads you need to bed them. Check out the Baer website for their instructions.
the reason I said not the most practical route is with the stock block, 400-425 whp is the limit on average. The blower itself will get you there with out heads and cams. If you have heads and cams, throw on a blower and internal damage occurs, there is a good chance that heads will be damaged...
from seeing your other posts on this site and other boards, why don't you build your motor and not buy this GT. This way you won't have to worry about its longevity.
I would go drive it, sounds like a good deal. My auto holds up just fine and will take a lot more abuse. It has a tranny cooler so i wouldn't worry about it.
put the temp sensor after the blower discharge. the MAF connector has two wires that need to be disconnected and those two wires attach to the temp sensor. get the temp sensor from a ford dealer for cheap. Search on some other forums for pics.