I bought a ton of stuff for my car. I will give you my best advices. I wanted to go back to check the car but the information is not there anymore on your link.
1) Not sure if the car has gears but you'll definately some. Dont even know if the car is auto or manual. If auto, get some 4:10's or 4:30's. If manual, I'd recommend 3:73's, 3:90's (Mine..) or 4:10's. Again..I dont know your plans for your car. Because I planned to go nitrous, I didnt wanna get higher than 3:90's. If I'd stayed N/A, I would of bought some 4:30's. And I have a 5speed. I see that you will drive the stang in the snow...Gears will make you spin a lot more..
2)Not sure where you live and if you care about the laws, but an off-road H-Pipe or X-Pipe is a good mod. You'll pick up a few ponies. I have the O/R H-Pipe from BBk with the longtube headers. A good catback would be good as well. I recommend Magnaflow.
3)Underdrive pulleys is the best bang for the bucks(everybody says that). Cheap and you'll gain more power.
4)You need tires(summer). I had very good launches lately with the BFG Drag radials. But my next tires would either be the Mickey Thompson Drag radials or ET street.
Subframe connectors (full frame + welded) helped the stability of the car a lot. I should of done that mod in the beginning. I'd start with those mods if I were you. Lets see what the others will say.