First off "catback" means the piping/exhaust from the cat back hence the name, if u know wat the cat and all the other stuff is u should be able to work out that u will just be getting the piping from the cat back and most prob the muffler as well. The order i would go is get the catback system first then the extractors and then the high-flow cat if there is any use. And i would think ur civic would have a smaller exhaust then a 2" and yes it would be a waste getting the muffler and all the other stuff to fit ur stock exhaust when u are better off getting the catback and working on from there.