If your wanting that much power, you'll soon enough be talkin about changing the turbo to a gt28 or gt30 conversion. Its gonna cost u a good couple of grand t have it done but results will please u. Before hand i would say just do the usual tried and tested stainless exhaust and k&n filter route. Then a de-cat pipe and possibly a set of uprated plug (denso's???, sure someone wil correct me), and a set of uprated leads.

On a sidenote, i went with a couple of mates in their focus rs's to a rolling road day at SCC. One had a k&n kit and decat and bluefin (i think), the other was completely standard, and they made same power.