I was within 3 seconds of some s2000's ( a lot I know, but they're freaking S2000's) and beating some BMW's today. I have a pretty much stock engine, but highly modified suspension. I would love to have your engine. I could probably take them then.
I would suggest that you first get some actual time behind the wheel at some events. This was only my second event and I was running in the novice class. Talk to the instructors, they are their to help and teach you.
A decent suspension upgrade is the tokico HP shocks and tokico springs, along with a swaybar kit. That and your 15" tires should defiantly get you going. Hawk also makes pads for 280zx brakes just search for them. Everything I just listed is literally just remove and replace.