Who cares about rubbing?
If you do rub, you'll rub the fender liner. IF that's the case, after a few K miles, you'll rub through it. Problem solved no rubbing.
Wheel size doesn't matter. (meaning 17 vs 18")
You'd have to mainly look at width of the wheel, offset, and width of the tire.
Don't be a wuss and get some 18s
-J
