Legacy rotors > WRX rotors in the back, which pushes the brake bias rearwards - stock brake bias is safety oriented, and thus will always always lock up the fronts first. As for intake - it's all about air flow, and you can only push out air that actually came into the engine. Velocity and pressure is the key to power - high velocity and low pressure is the best but with N/A, you can only compromise and tune for a certain RPM range. Also, if you do a CAI, you get cooler air = denser air = more power.
Again, figure out your end goal and mod accordingly - N/A and turbo don't have a lot of good common parts as you push for the performance envelope. If you have the money, buying a full wreck of a JDM car and swap probably nets you the best gain for a 93L