if i buy a full catback system, do they genreally include the cat converter? and if i decide 2 put headers a few weeks later after putting my cat if i decidee to put headers can i buy any headers that fit my car or do they have to be compatibile with my cat?

 

I think cat-back means just the part after the cat. I dont think it includes a cat.

 

when i buy a new performance cat back system i have to buy i catalytic converter thats performance or can i use the oem cat converter?

 

You should be able to use your oem cat. But if you want you can pick up a high flow cat for pretty cheap.