If you want to get the most out of the system, you really only need headers. The intake side is already being addressed by putting on the supercharger. Chances are mods like a ported manifold or spacers wouldn't even be a difference compared to what the supercharger does for you. So I wouldn't really waste money on those. If you want to do them, by all means do them but I don't feel their needed. That then leaves the exhaust side of it needing to be worked on. So to free up exhaust, get headers, some good quality cats and you already have an axle back so you're good there.
Another thing is whether your car is a manual or auto? If it's a manual, you might want to start saving money for an aftermarket clutch. If auto, start with suspension. Like Ventmaster said, look into a nice sway bar package to keep the rear in check. As well as subframe bushings to further aid that.