if you're looking for the Nismo cat-back try dooing some googling and see if there is anyone selling other than the stealership b/c they charge like near 1g just for the exhaust, not counting labor. If Lee's Auto-parts sells the 2010 Exhaust then that is probably a good place to look.
As for the Y-Pipe, go with racinglineperformance.com, they are a NICO sponsor and have a lotta nice goodies for the A/C. (for the record im assuming he says its a must because it sounds so sexy, not b/c it is necessary to achieve proper fitment, b/c the nismo exhaust would be a direct factory rep. for the OEM exhaust so the Y-Pipe is not necessary from that stand point.
As for an intake, its all about how much you want to spend, but check reviews online as for everything youd want to buy to see other's results. I'd recommend AEM since they make it for the 3.5 only, or K&N, and maybe third would be Injen.
Lastly, for CMOD, I think that it would look good but its all up to you when it comes to aasthetic mods, b/c you need to be happy with your car more than trying to make other people happy.
Hope this helps...
