2005 aveo exhaust questions.

Hi, I'm thinking of changing some thing in the exhaust department on my stock aveo. I have installed a cai, I was planning on putting in a flowmaster 40series delta flow muffler as well as later on a hiflow rear cat. I believe the stock exhaust pipes have a resonator mabey two in it, would deleting it or those with a straight pipe make better airflow as well as help the muffler pronounce itself better? I'm also doing all this to help increase horsepower and torque at highway speeds. Last question, is it street legal to change out the original header/cat assembly for a straight cat deleting header? Per if I could find that for my engine.