Ok, heres some tips

1. www.thevboard.com is going to become a very good resource for you.

2.If your looking for an exhaust for the car that is subdued in its looks and sound then Apex'i WS2 Cat Back or the Stromung Cat back will prob be the 2 choices you have to look at, they both maintain a stock look pretty much and the stromung is nearly identical looking minus the polished muffler to the stock exhaust.

3. Nismo CAI typically adds about 8 - 10hp. Header will probably add around 15 - 17hp, the down pipe will add somewhere around maybe 5hp. And a full cat back exhaust will prob only tack on about 2 - 3 hp because the stock system is already extremely free flowing.

HOWEVER, if you run the CAI, Header, and Downpipe thru the stock exhaust its going to sound like you have a pack of 1000 Bee's coming out of your exhaust. You can go to that site that I gave you, www.thevboard.com and look on there and find numerous people that tryed to run with the stock exhaust and it sounded worse than a Civic with a pepboys muffler freshly welded on.

If the catback exhaust you get is still too loud just take it to a muffler shop and have another resonator welded into it, I believe the WS2 from apex'i comes with one welded on. I have the N1 apex'i catback exhaust and it came to me with a 12inch resonator already welded on.

If and when you do get the car fully bolted you can expect it to run in the neighbor hood of low 15's to mid high 14's in the quarter.

Hope this helps