I'm glad to see you are doing your research. It can kind of wear you out, but at the end you'll know what you want and what you're willing to pay and be ready to jump on the right one when it comes around. In my experience, buyers remorse happens much more often on impulse purchases.
I haven't had any experience with swapping wheels, but I will say that the car is disinclined to put more power down than the wheels can handle. The traction and stability control systems seem to kick in easily. So I don't think the 18s would be an issue there, unless you were worried about maybe losing a second on takeoff.
(Maybe this would be different if you drove it in Sport mode. I never do, so I'm not sure. The way Sport turns the dash display red just hurts my eyes.)
Since I got my radio/nav system up and going, it's been trouble-free (knock on real poplar wood trim). I haven't had the lockup problems a lot of the members have.
Not sure why you are having trouble seeing the whole model year chart. It's just a JPG file--if you right click, you should be able to download & save it and look at it in Microsoft Paint or something similar.
Keep us posted on your progress. It's always interesting when one of the members is looking to buy.
2016 V8 VIP+, black with white interior