With my car not lowered, I got 18x8. For the tires, I wanted something wider, so instead of the 225 width, I got 235 (some get 245--if so, you may want 18x8.5). Actually, now that I think about it, the tire walls may rub your inner wheel well w/ 8.5's, because my rears are pretty close.
Anyways, I wanted to keep the same overall profile so that my speedometer would still be accurate. Therefore, my tire is 235/40/18. Like I said before, there isn't much clearance with the rear tires...so, a 45 profile may not even be an option (esp since you lowered).
BTW, how do you like your dinan upgrade. I believe they're a bit pricey, so is it worth the $?