Already a lot of great advice given, but here is my input:
- as many have said, since you already have a BBK, get some track pads. I love my Pagid yellow 19, even if pricey.
- R3 head and neck restraint from Simpson (or similar) - SAFETY FIRST http://simpsonraceproducts.com/head-neck/r3.html
- you do not need R-compounds (yet), but I would think that getting a square set of the 18"x10 ET25 Apex ARC-8s or EC-7s now, with some Dunlop Star Spec or Bridgestone RE11 or Yokohama AD08 (whatever comes in 275-35-18) would be a great way of spending your money. Get 5 or 6 wheels so that you can rotate your tires and only need to travel with 1-2 spare in your car.
- may be some camber plates to get the best of both worlds: DD and Track set up.
- lastly, in order to be strapped in your OEM seat: before you enter the track, tilt your seat backwards, pull on the seat belt to lock it and move your seat forward again so as to keep the seat belt locked and tight on you. You may have to adjust this by repeating the sequence if you were too far or forward when you pulled on the belt. Works great for me and will be good until I decide to make the car a dedicated track car with bucket seats.
- lastly, read books on track driving (ie, Going Faster or Speed Secrets, etc.) and devise a learning plan on which you will be working to acquire the proper skills. Data logging tools like Harry's Lap Timer on iPhones seems a great way to measure your progress.