intake is the best place to start with the focus. Most do Short Ram Intakes for their cars ( i prefer my MAC SRI). Then definitaly do an exhaust. 4-1 Headers, High-flow cat., 2.5 in flex pipe, and full 2.5 exhaust.
Unless you want to go suspension. DONT drop your focus too low. I did the SVT suspension kit and thats perfect for my rims. (Look in my photo gallery).
Oh and brakes will make your ride a fun little thing!
there are a bunch of How-To's and stuff at the top of the zetec tuning page. They go through all of the intakes, exhaust, pros and cons to long tube and short tube header and all of the fun stuff you can do to your car.
exhaust depends on style...you can get a borla, magnaflow , focus sport, hypnotic illusions and have a OEM style, or get an Apexi World Class 2, or an HKS Catback, or even Thermal. the last 3 are cannister style i believe. i have the HKS. i love the looks and sound. it has a big angle. I would get the svt header, well, i have an svt, and i have heard that they are rpetty much one of the best flowing for the money. and then, maybe get an offroad pipe, which takes out your catalytic converter.
The best things or the first things I would get is : AEM Cold Air Intake, VF Engineering Rear Motor Mount, Steeda Tri-Ax Short Throw Shifter, and a Tune (Hypnotic Illusions, or Focus Power) I have the Hypnotic Tune.
exhuast is all about restriction. our stock 2 inch is rather very restrictive. If you go 2.5 in piping, you should have to have enough power pushing out of your engine to compensate and create enough back pressure (yes you need some restriction). So if your doing lite modding, go with pacesetter. its 2.25in and rather quiet. Adding headers and flex pipe will raise sound a little bit, but again, dont go too big without backing it up with enough power
lets see...what else do you have questions about? i know a bit about cars and tuning. learning a heck of a lot about the focus' on this site though. i do all the work myself so if i f-up i know what i dont want to do next time lol
The SRI's are good, i went with a full cold air intake by AEM, i dont regret it. i also have an SVT, so the design may be slightly different. but either way, i choose the full cold air intake over the short ram.
After intake, grab a shifter and a rear motor mount, then get a tune. he tune can always be upgraded. the motor mount is so worth it. it is awsome. you wont believe how much more firm your shifts will feel with the VF Engineering Rear Motor mount. it is a billet mount with Urethane Inserts.
remember 02SVTsilverstreak he said he is an auto, so i would try to make a little more power before you need motor mounts. and he is an auto so i dont know how much it would help in the beginning. Same auto comment goes with short shifter lol.
with an auto, i would go exhaust and throttle body before tune. i want a throttle body SO freakin bad on my car but i just got an offer for someone to buy it...thinking...
my bad on the auto. i havent driven one yet, well, atleast floored it in one yet. no matter what, the mounts are benificial, but for an auto, i cant see it being as big of a deal to it being an auto. saying that, the next thing i would do for it would be a tune, and adjust the shift points. that will make the car come more alive than it is now.