im not saying they are the only way to go, but When you think about bodykits they make some good stuff that is truly designed for Time attack. If your car is a daily driver stick with the stock body with a nice front lip, and JDM evo 9 rear bumper. If you want the crazy aero stuff you are going to need a full coilover setup very wide wheels with lots of rolling pulling and cutting of the fenders to compliment the aero. I had my car almost how i wanted the exterior then a curb claimed my CF front lip and a wheel.
My next car will not be for the faint of heart in the aero department. much like yourself I will have a Time attack ready street monster. more detail hopefully in the near future but it will be a full build fromt top to bottem.