As far as performance upgrades go you are in the right section. But the sound system upgrade is a different section, so be sure you post anything you need in the Car Audio, SYNC and Electronics
Exhaust is a good route to start on. But what we really need to start with is your budget and what results you are looking for. Let us know what you have to spend and what you would like and most of us can help point you in the right direction.
Also, the blue text is a clicky for the audio section.