Since you are a 4th gen, you only have 2 options for headers...JBA shorty headers or ARH Longtube headers. The ARH's are going to make more power, but they come at a price. BBK is supposed to bereleasing their new style 4th gen headers in the next week or 2, and they are going to be the cheapest option. The JBA's and ARH's are made of stainless steel, and the BBK's are mild steel.
As for the muffler, the 14" sounds great. I ran one on my 03 and was very happy with the sound. Not too loud, but definately not stock. If drone is an issue for you, then I would leave the stock resonators in place with that muffler.