The Nismo cat back is the way to go, much heavier than the OEM, easy to install, good sound lower backpressure. All of the things that you want in an exhaust.
If you can swing it do set of thorleys, and the nismo cat back at the same time, I would recomend getting CEL eliminators but that is up to you. If you dont mind the orange CEL lit up all of the time dont worry about them. If you do they are easy to install while you have everything appart.