I'm going to take a different approach - You are asking about and people are talking about parts. I'm going to say you don't need to do a damn thing but just sign up and go. Your car as it sits is more prepped than 90% of what shows up at a local autox, and is surely capable of exceeding your abilities (nothing personal, just a reality that it takes seat time to even scratch the surface of a car's ability). So my advice is to find a local club and sign up and go. A Starting Line school (
http://www.sccastartingline.com/) would be a good thing to invest in as well, but even that I would not put ahead of just finding the next event you can and attending.
I'm not saying don't buy parts - It's fun. But I am saying don't let your level of prep dictate whether you / your car is ready. Thousands of people a year show up and have a blast in boring grocery getters. Dive in!