18x8 with a +40 offset will fit. It's been done on here a bunch of times before. No problems, especially if your not dropped. Just don't go with huge tires (bigger than 235/40).
19x8.5 with a +30 offset will stick out a little pass the fenders (in front) and you'll probably end up rubbing on corners and bumps in the rear.
19x8.5 with a +40 offset seems a little sketchy in the front also, but not as bad as with a +30 offset. The rear might be okay however, depending on the tire size you go with.
When shopping for wheels, I suggest you go into the picture threads, see what everyone is running and what sizes, and do the estimations you need to what you want.
