Welcome to FF!
Regarding performance, it depends on your budget. You can pick up a jackson racing supercharger for ~$1500 these days that will get you about 80hp, and the JRSC's can be carb legal if you get one with the sticker.
You can also get a turbo kit with FSwerks that will put you around 230hp at the wheels, which will make you faster than most WRX subies (not STIs). http://fswerks.com/zetec-turbocharger.htm
If you dont want to go FI, or dont have the money, then your first and best mod is to get some better suspension. I recommend KYB adjustables, and H&R Race springs. Those will make your focus handle like its on rails. In terms of performance, that's your best bang for the buck.
Engine-bay wise, grab a SVT header, CAI, and a FSWERKS Stealth Cat-back, and call it a day. That will net you about 20hp, and give your car a mean exhaust note.
regarding chips, the only option with foci is to get a proper tune. Go get a SCT Xcal 3, and find a tuner to do you right. FSWERKS is local and knows how to do things right.
Come out to the meets sometimes!