Replying to So all you WRX guys out there....

I have an 04 WRX wagon, and I'm starting to get interested in all the mods out there but I know very little about cars.  I would like to take a look at doing something that could upgrade horsepower and/or fuel economy, but I really don't even know where to start.  (Nothing to crazy expensive to start, and I would rather it be something that isn't going to kill my ability to sell if I chose to do so).  So basically my questions are:

-What's the best project to get your feet wet for a newb (I will have help from a knowledgeable person for sure, so don't worry)

-I looked at performance chips and exhaust systems, any comments on practicality, cost, or recommended items?

-Anything out there I should look at that I didn't mention, and about how much HP could I add with some of this simple stuff?

Thanks a ton in advance, and for the record I looked at Scoobymods, I'm just not sure where to even start on that site.  Maybe I missed a thread that explains all this...