If you're going to run our 18x8.5 ET45/18x9.5 ET50, we recommend the 225/40/18 and 255/35/18 tire sizing. You shouldn't have issues with that setup. I wouldn't recommend spacers with them though, since they're already pretty flush. You would need to do some fender work to push them out more with those tire specs.
We always recommend that you measure to see how much clearance you have to work with.
