Alright, so from what I've gathered you've had a cavalier that you haven't been able to drive much.
Now that you've got an RS, you have the ability to avoid those things.
Reliability
No down time
Versatility
These are the things that would be the goal to shoot for. Forget looks stuff, forget performance stuff. Cover your bases first.
1. Make sure maintenance is up to date. Oil change, transmission oil change, rear diff oil change, spark plugs, wires, fuel filter, PCV valve, air filter, cabin air filter, make sure the coolants clean, inspect the brakes, inspect the power steering fluid, etc etc etc.
2. TIRES. TIRES TIRES TIRES
TIRES. Inspect the tires the car comes with. They're probably all seasons. All seasons are ok, but you can really step up your game by getting a separate set of wheels and running snow tires in the winter.
3. Comfort. Like the stereo? Good keep it. If you don't upgrade. Seats uncomfortable? Upgrade those. A comfortable car makes spending time in it much more enjoyable.
4. Driving. Why throw money at your car on upgrades when you can just upgrade the driver. Yes! You yourself can be an upgrade. Some seat time at an autocross, a rally cross, etc can teach you a lot about driving and make you a safer (and faster) driver. Plus you'll have more fun doing it! A day of racin' beats a day of sanding and painting!
After all that, you can do little tweaks like a swaybar here, some bushings there, short shifter, etc.
RS's have a lot of potential, they're deceptively zippy, and can bring the business better than most STi's at a rallycross
I've had barrels of fun with my RS DEAD STOCK. I didn't start messing with "upgrades" until owning it for 4 or 5 years. You don't have to.
If you really want to be a unique snowflake and make your car look pretty and different, you've picked a very expensive way to express yourself, and I wish you luck, it's just not the route I'd take. I'm a driver not an artist.