Need a lil help

Im going to buy a header not sure which to buy thinking about aerospeed there. Then im going to get a custom pipe made 2 1/2" inch all the way to the muffler and im taking the cat off im not sure if that will be okay tho need some help there. i think i am going to either get a greddy muffler or a 5zigen or thermalrd not sure which to get. if anyone has some suggestions plz help me out muchthanx