Does the car have an automatic or manual transmission?

If it has a manual transmission, get a short-throw shift kit. It will reduce the throw between gears, making changing gears faster and more fun. It will also give your car a more sportier feel. It is cheaper then exhaust and intake. For intake, I would advise that you NOT get a CAI that draws air from right in front of the tire. The reason for this is that whenever it rains hard and you travel on roadways with standing water, you risk sucking in water, which will hurt your engine. Depending on the intake system, you can switch between CAI and Short-Ram whenever this situation arises. If you don't want to worry about wrenching on ur intake system whenever a few clouds get into the sky, then just get a Short-ram intake system.

When it comes to getting an exhaust system, get one that was designed just for your car, not a universal one. Also get one that is bolt-on in case the NOVA cops want you to change your exhaust back to stock. If you're going to lower the car, make sure you replace the shocks in addition to your springs. Failure to swap shocks when you swap springs will possibly cause the shocks to explode b/c they weren't designed to stay more compressed with the new springs.

In concerns to sound system, headunit should be swapped before speakers. If the speakers still sound like crap after you have the new headunit, then swap speakers.