Anything you do to clean your 350Z dash will eventually end up with wear marks as the paint rubs off easily. So the best thing to do is to take it out and respray it with a nice matt clear coat to finish it.
In the short term though most dash cleanders should be OK, but someone like @ilogikal1 or @SuperStu will probably give you the best advice on really good products.
As for stereos there are loads of double din units that you could put in, it really depends what you want. Touch screen or not / android compatible / apple car play compatible, budget, etc. If you let people know what you're looking for more specifically they've a better chance of helping you find what you want.