[Mk3FirstCar-Mike]

First off, I'm going to say that most teenagers are going to at least be in a minor car wreck. It's recommended that you get a cheaper, slower car to start with so you gain experience. On that note, if you still decide to get an older sports car(As I did, however I still have an older, cheaper car to start with for the first year)
Take this into consideration: RX-7s are rarely maintained well and the rotary engines are nice, but not if you want loads of power. That being said, if you do get one, make sure it's been well-maintained.
The AE86 is preposterously rare, probably more expensive than the others. It's also fairly... well.. slow at stock settings. Meaning you won't be getting the most horsepower for your money. They are, however, fairly fun to drive, as I've been told on many occasions.
240sx's are also fairly slow at stock settings and don't really have a whole lot of potential for power without an engine swap or a turbo. They do, however come fairly cheap in the first place and have plenty of available upgrades.
MKII's and MKIII's come with a decent amount of power and the possibilities for their engines are fairly high, but as they're meant to be grand-touring cars, they're heavy (MKIII's are 3400lbs).The weight of them makes them a little harder to begin drifting, but at the same time, much more predictable while doing so.

As for your upgrades: Coilovers are a good place to start, but if you're going to get them, don't cheap out. By that I mean, you'd might as well save for them and get a $1500+ set that IS REBUILDABLE. Some people say that it's best to get an average, cheap set simply to experience the difference, but even those are over $500 and I can't in all good sense, tell somebody to waste money on them. Tein is another thing to stay away from. I can honestly say that I have NEVER heard andbody who knows suspension tell me that they like Tein. HKS and Apexi` would be good brands. Coilovers come in a set and completely replace the shock/strut, spring and the "bar." Keep in mind not to get a set that is overly stiff, though, or you will lose all comfort you had while street driving.
Sway-bars are nice to get, you can probably get a set for around $300.
Brake-Pads.... You know wut-do. Etc..etc..
Aluminum Fly-Wheels will reduce the time that it takes the car to rev, providing better, and more responsive power through the entire range. However, they do require that you dismantle part of your transmission to install. An aluminum drive-shaft would have roughly the same effect for about the same cost, with more ease-of-installation, but you pick whatcha-want.
As for the clutch, they are rated for certain amounts of torque and you really wouldn't need to get a stronger one until you get more power and begin thrashing your car through corners.

If you've got any questions, or I said something stupid(I probably did) feel free to ask or yell at me.