the g35 sedan has a +45 offset, which is an offset usually found on FWD cars, yes
18x7.5 most people are going with a +42 offset.
U R spending a whole lot of money on rims and tires, take the time to learn what each number in the measurements means.
Learn how to calculate tire diameter, revs/mile, offset from the fender lip, etc from parameters given like 225/50/WR17 and offset, bolt pattern, rim, section and tread width measurements. A salesman may have too many of one type of wheel and is trying to sell you "anything that works" but might end up looking goofy as hell