Jeff,
First of all, WELCOME to the site!
Second, you stole my car man! I just saw mine in the shop yesterday. Today they tell me that she needs a new torque convertor. Come to find out, they sold it to you. Oh wait! You only have 55k and I have 150k. You have the pin strip and I don't. Ok, we are still cool!
As Andy said, search search search. If you have an idea or question, just search the forums for it like you would on Google. You will be amazed at the amount of knowledge locked in this site! If you can't find it, then feel free to post it here. Be as specific as you can. One thing that you will learn here is this, "Do not be afriad to ask a question, but if you have looked into it some first."
Follow Prans advice and start with the exhuast. Maybe a muffler first. A lot of people around here like the Flowmaster 40 series! Do not worry so much about the resonator right now. Most of what you read in the FAQ and Mods section is for the SVT. They have a different pipe size and that is a whole other story. Remember that search thing? You will find a great deal on it there!. Then do the K&N drop in if you like, but I fill that it would be better to get a "Cone" Air Intake. Invest the money now, so that when you get the SVT exhaust or MSDS headers, it can really breath. Remember to search! There is a ton of this around in here too! Just type "exhaust" and you will have enough toliet reading material to last a life time.
Remember one thing first and foremost, "Function over Form!". Don't waste your money right now on things that make your car look different. Unless maybe the Roush Cougar springs (Search!
) or the BAT EuroKit. These funtion. Basically, stay with what makes your car perform better and not what makes it look better. If you go out and spend all your money on looky stuff, we call that RICE and don't really like that around here. But to each his own, as most would say.
Good luck and I really hope you enjoy your Mystique as I have mine.
P.S. Where are you from anyway.