00' GT Exhaust????
#2
Cat backs and mid-pipes net you nothing, basically. If you want power from an exhaust, gotta go w/ long tube headers, which are costly and/or time consuming. Best bang for you buck at the price of a cat back is going to be gears or suspension work.
#5
Gears mean switching your ring and pinion gear set (in the rear end) to something that is numerically higher, which allows for better acceleration. As for cost, just do a quick search on the topic and you'll get tons of posts on this relating to what ratio and the cost.
#7
depending on how large of a drop you will need CC plates. Typically 1.5-2" you will need cc plates
#9
I'd go to Maximum Motorsports for a package. When I said suspension, I meant stuff like brakes and rear control arms since replacing those provide a benefit. Lowering your not so much but if you want that, MM has packages w/ H&R springs which are better than Eibach.