Rally : I believe the Steeda springs are progressive rate. I've also heard mixed arguments about whether caster/camber plates are essential with springs. I just figured for an additional $150 it wasnt worth risking a bad alignment without them. Redline suggested them also.
Mustang exhaust is divided into 3 parts. First are the headers. There is a fair amount of restriction here, but aftermarket headers for the 4.6 are expensive, and hard to install. Next up is the catpipe with the cataylitic converters. When I switched in the Bassani pipe for the stock catpipe, I felt a HUGE gain. After the catpipe is the catback system. This contains the mufflers and the tailpipes. By switching this system out, you won't gain much horsepower, but most people just do it because an aftermarket system will give the mustang that awesome rumble. If you're doing anything exhaust related, go see Tony at Mel's Mufflers and tell him Jason sent you. Good luck.
And don't worry about asking questions. If I had asked more questions before buying impulsively, I would have saved a lot of cash. If you set up a plan leading up to where you eventually want your stang to be, you'll save a lot of time and money. For example, pulleys will not work with a supercharger, so if you're going to supercharge it, do not put pulleys on in the meantime. Some parts clash, so always keep the greater goal in mind.
Last, when my intake blew on my 97 GT, I layed the guilt trip on Ford and traded it in on the 2000!
