If you get a full exhaust system, your CEL will turn on and you car will run like shit unless you get a tune or get the Akrapovic "Delete-R". I would recommend you the Akrapovic Evolution Exhaust System and ESS have a special tune for this system. If you need any parts or question call RENN SPEC ask for Jason.
And never trust a salesman, most of them don't know shit about anything. They will said whatever it takes to get it sold.
Tune and pulley will void the engine warranty.