I like to think I'm fairly knowledgeable about wheels. My 2 cents, wait until the car comes out and people get their hands on them so you ensure you get wheels that fit correctly. If you want to order now, I would go with the specs that match what people run on the 370. For volks that's 19x9.5 +22 front and 19x10.5 +12 rear, that will fit stock suspension and wont rub. One other thing to note, unless these are in stock you are likely looking at 6-8 months wait from Japan.
Quick rundown for you. Height and width are fairly self explanatory, offset is the distance from the center of the wheel to the back of the face where it would sit against the hub, so +22 would mean that the back plate is 22 mm from the center seeing as it's a positive number, you can have negative offsets which means this is a negative distance from the center as well.
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Personally I'm going for a set of Rays gram lights, they are still a great quality wheel and about half the price of the ze40's, not forged unfortunately, but still quality.
There's also going to be a Z at the yorkdale mall from Feb 3 to the end of February, I'm hoping you can get close enough to it, because I am going to be bringing a tape measure to take some measurements for wheel specs.