As others have said, tires, brakes, safety stuff, etc.
Before you do car performance mods, do driver performance mods. In other words performance driving school.
No matter how poor your Porsche might be in performance (which it is not!), unless you have had a bunch of driving instruction, you will not drive it anywhere near its stock capabilities.
Go to a driving school and if they have timed laps, I would bet no matter what your best lap time is an instructor will beat it by a few seconds in your car.
Also if you are considering performance mods and plan on doing AX or track, what you can and cannot do will be governed a bit by the rules and what class you plan to run in.
Dont mess with mods at first and dont end up with something like this:
https://www.youtube.com/watch?v=bQptfdSCdhs