Welcome,
In regards to the brakes, the stock rotors are fine for driving on the street and many people think that the stock plain rotors are fine for the track. Stainless Steel brake lines will improve you pedal feel. The cheapest "upgrade" to the brakes is probably changing to a more performance oriented pad and maybe upgraded brake fluid.
Serious upgrades will cost big bucks (Big Brake Kit) or even changing to a larger rotor and caliper that fit (some people do this and its cheaper) but make sure to do some research first, cause if you get the wrong stuff it won't work.