So many good suggestions, but ultimately it will depend on what your final endpoint goal is. I would say good tires is the first place to start. No matter what you plan on doing, pushing the S is something we all do and good tires will help keep you safe (to some extent).

Then start with the small touches to personalize your car: stereo and interior work.

If you are already happy with that, then start with possible body work like a lip, wing/spoiler, hood, rims, etc.

If you are serious about getting some speed out of it, an intake, exhaust and test pipe will prove beneficial, especially with a tune. I would only go that route with the bolt ons if you really plan to put some work into the car including FI. I have a few more aesthetic mods to go before I save up for a small FI project, but the bolt ons I got (with the exception of the FIPK) were purchased based on going FI in the future.

Most importantly, have fun with the car and make it your own!