On your car, you want to get the header. The exhaust manifold is really restrictive. They are calling the an adapter pipe a downpipe on that page, but that is not a very good description. Causes confusion. Get the header, use the stock cat for now, and get the catback. Later you can get a Random Tech high-flow cat.

Exhaust is where you make your power on the rotary. The ONLY reason that you would stay with the stock exhaust manifold is if you just want to keep the car quiet. Headers will make it louder.