If the car is still fun to driv, then I would wait on performance mods, just because it takes a lot of money to make the Focus fast. I would do audio then wheels and drop and then do performance mods. Do the exhaust and header at the same time then do an SRI and go from there.
The main reason why I would hold out on the performance is cause you'll still get beat unless you're boosted. When you lose interest in driving it, the fun will come back with a few bolt-ons like intake and exhaust.
Hatch Nation #8
September 2012 Ride of the Month