[StormTrooper]

your car has two "cats" in the exhaust system. these are for emissions which i would assume are strict in new york.

the benefits to replacing the exhaust is to free up flow ( the header is more complicated than just bigger piping)

Getting just a catback will have little to no affect on power or mileage, it will make it sound different (usually louder and deeper tone)

Resonated will cancel out certain frequencies generally to avoid drone when switching to an aftermarket header.