For handling, I would get a set of 18" factory wheels and a set of quality tires. Drive the car for several months and see if that is how you want it to handle.
If it were me, I would stop there but this is a matter of taste. The S with 18" wheels is among the best handling cars in the world just that way. It may be enough for you.
The stereo upgrades sound great.
Best of luck to you!