IMO 18's look stupid. We had a set on my friends car and it wasn't lowered and now she's rolling with my stock 15's
225/45/18 are too big and I think you'll find they'll rub. I have 17's and they look nice, 16's are great too.
I would say the 17s as well. Here's my set. Enkei F-1s on Yokohama Avid H4s':
IMO... it's a proper fit. I actually drive on them, all year long. Of course.. you willl feel the bumps alot more... but it gives it a incredible look, drives wonderfully, and I absolutely enjoy them.
If you fall, then get back up........Luck favors the prepared