Alright I'm gonna try and post at the same time as Kevin, let's see how close our responses are.
First off, welcome to the board. Nice to have another old schooler around.
Be sure to come to the meet on thurs.
A. Wheels & Tires --- Get some 16s. You can find WRX take-offs for around $200 with stock tires, there is someone selling 6 2000 (6 spoke RS) 16s (wider than WRX wheels) for $225 with tires. They will give better performance but most importantly you can fit bigger brakes under there. They also won't bend like a steelie.
B. Suspension --- You can get a WRX rear swaybar for cheap or free and it will make a big difference. A swaybar with endlinks and some new rims and tires will really transform the car. You will have less articulation off-road though. Steering rack bushings from whiteline are also a cheap and noticable upgrade. If you want something more aggressive you can opt for a ground control and KYB AGX setup. You will have better handling and you can even raise the car if you wish. Probably around $700 more if you want top mounts, which you should get.
C. Interior --- WRX seats are nice upgrade. Of course they won't match your interior. They do drop right in though and are much better than your stockers. You need a short shifter. Buy a Kartboy with bushings. It's damn short though. I have stock RS shifter you can have for $10 if you want it.
That should be fine for now.
D. Exterior --- Clear corners are cheap and make a big difference. There are optional fogs for your car but that would be quite a bit of money for a minor upgrade if you ask me. You can also fit a 2.5RS front bumper to your car. You can fit an RS hood too. Many people forget the 97+ OBS came with the same hood, it also came in forest green so you should be able to find one that matches. An RS bumper swap with some upgraded lights will improve looks and give you more lighting.
E. Engine --- You won't get a lot of power out of her without forced induction. I'd save this for last to be frank. An intake ane exhaust will help but money is better spent elsewhere at least initially IMHO.
F. Drivetrain --- Clutch and flywheel will make a big difference. Exedy makes a nice mild upgrade. LSD would be expensive for it's limited benefits on a low hp car like your IMO.
G. Brakes --- WRX front brake upgrade will be ideal. You will need at least 16s for it. You can swap the rear brakes I'm not sure what all you need to be honest. Mind as well go with the H6 rears while you are at it. Make sure you get SS line, a decent fluid, and nice pads while you do it.