well i cant help you on the sound system and appearance aspect since my can looks like frankenstein's monster and doesnt really have any sound except for exhaust lol. but power i can help you with.
the only way you are going to get a power upgrade with this car is to go with some kind of forced induction. supercharger, nitrous, or turbo. otherwise if you want to try to build the car for more power and stay naturally aspired you will be spending twice the money for a quarter to half the power.
as far as bolt ons go the best route is the SVT header conversion which requires a SVT header, SVT cat or off-road pipe, SVT flex pipe, SVT dipstick tube, and either alot of header wrap or a relocated power steering line. sounds like a lot but it isnt that bad to change all that out.
dont bother with the exhaust unless you go up to at least 2.5 inch diameter piping from the flex pipe back. if you get the SVT header you want the exhaust to flow as freely as possible. the car would make the most power running open header with the SVT header if you could get away with it for emissions and noise. so the less restrictive you can make the exhaust the better off you are.
put a K&N panel filter in the stock air box or locate a SVT airbox and snorkel and get a K&N for it. the SVT is only slightly better than stock but is still better than 90% of the aftermarket intakes that get heatsoak so bad that the factory intake outperforms them.
nitrous is the absolute biggest bang for your buck power adder that you can get for the focus. i happen to be selling a kit in the buy/sell/trade section of this site if you're interested. a little copy and paste snippit from it:
you get more power per dollar spent with a nitrous kit like this than with any other mod you can think of.
buy this kit and run a 100 shot (which the stock motor can handle fine with a good tune) which will make roughly 100hp more. that is $6 per hp.
a SVT header conversion costs about $500 and makes about a 20hp gain which is about $25 per hp.
your average new complete turbo kit costs around $3000 and can push hp up by as much as 140 on a stock engine. that costs about $22 per hp.
dont get me started on those underdrive pulleys that cost $100 and maybe make a 1/2 hp gain.
need i go on?
there are turbocharger and supercharger kits for sale as well on this site for under $2000. if you do any of that you will absolutely NEED a tune. Tom is our resident go to guy for tuning on the focus. his screen name on here is 1turbofocus and he is damn good at what he does.
focus-power P&P head $1100
focus-power DIY turbo kit $1495
tom's first time in Vegas? PRICELESS!
Originally Posted by 1turbofocus
I love this big little city HOOTERS !
Every time you drink a beer somewhere an ugly woman becomes beautiful, so get to it!