First off, congrats on having a Mark VIII as your first car! I'm sure you'll have alot of fun with it in years to come. Like has been mentioned before, take it slow with your mods at first. No harm in doing the freebies/cheapies (air silencer/resonator removal, drilled airbox, K&N filter, J-MOD, etc.), but as far as the bigger stuff, it can wait until you are fully comfortable driving your car as-is in spirited driving situations. As far as racing goes, I wouldn't commit myself to any races at this point. I know people in school are going to run their mouth about their cars to you, and you've got a nice car, so there's no reason not to come back at them when they start talking crap, but just don't let anyone push you into a race before you're really ready. I know you're going to want to test your car's limits, but do it SLOWLY. Don't be like me- I was just lucky I didn't total my Mark VIII and hurt myself when I first got it when I was 18 lol. I've seen alot of teenagers try to show off in their cars and end up wrecking their car and sometimes hurting themselves. My newest Mark VIII parts car came from a kid, about 18 or 19, who was driving 60 MPH in the rain on bad tires and ended up hydroplaning into a tree and destroying his car. Luckily, he was fine only because of the steel beam in the driver's door. The Mark VIII is a safe car, but don't let that go to your head, so you don't get in that "invincible" mindset alot of teenagers get into. Once you start driving, you'll figure out soon enough what your limits are and the limits of your car, and you have to respect those limits and don't push too hard.
Just trying to give a little advice from someone who was also a teenage driver with a Mark VIII when I was younger. Don't go out and hit 100 MPH on your first day with your car like I did. Don't try to throw it into sharp turns at high speeds, especially with stock suspension and stock-size tires- trust me, you'll end up in a high-speed drift, which sounds alot cooler than it actually is. Don't do too many burnouts or donuts- your tires will thank you. Like I said, just take it slow as you learn the limits of you as a driver and your car.
It's really cool for me to see teenagers still coming along who are interested in these cars. It was rare (basically non-existent around here) to see a young person driving a Mark VIII even back when I got mine in 2004, but I did get alot of people interested in them around here with races I'd won and all that, and a couple years after I graduated highschool, I did hear of a guy a few years younger than me who apparently knew who I was (I didn't recognize his name) who had got a red Mark VIII who would talk about my car getting him into Mark VIII's, so that was cool.