What wheel brand, model, offset and size. Also what tire size?

 

If you're looking to get aftermarket wheels have you considered 19s or 20s?
They won't cost too much more and you'll have the benefit of stiffer sidewalls
for cornering and tend to look better (at least IMO) on the Gs. Here's tireracks list of 18s that will fit your G.
Wheels for 2010 Infiniti G37 Sedan Journey Base Model Built on or after 3/2010