Welcome along bud, there are lots of decent exhausts on the market if you look on youtube there is a video of the 350z with different exhausts like scorpion, cobra & invidia to name a few, have a look and check out how they sound.
I do like darker wheels on the sunset, I have Rota GTR's not sure what the exact colour is but they are like a gunmetal grey.
have you thought about getting an aftermarket exhaust?
I have had bad experience with nissan dealers so i now refuse to use the main dealership, i take it to my local garage who is a japanese car specialist and its gets treated with the respect it deserves. I am not too bothered about the "Nissan" service stamp, my car gets serviced every 4/5k with all major changes by someone who takes care of the Z and not a major garage who leaves engine oil all over the bay and "forgets" to put engine oil cap back on.