There are some 18" wheels I want badly, but the problem I have is they only have them in 40mm offset instead of 45mm. Also the fronts would also have to be 18x8. Can I get away with this? Thanks.

 

They will stick out significantly. For my winter tires, I use 44mm offset but only 7" wide and they stick out. With 8", they will stick out yet another 1/2" beyond the 4mm more than mine.

 

Is our offset 45mm? It sucks, the wheels I want are 40mm. I am a dealer so I get a pretty good deal on some different ones. Of course I don't get deals on Volk wheels

 

We have different offsets front to back. The fronts, you will be OK. The backs stock have offsets closer to 60mm (I don't know the exact mm). If the car is not lowered, you should be fine. You'll get a bit more rock chipping of the rear fender area, that's all.
Also, your handling will be changed to some extent due to the "track" widths of the car being larger.

 

Stock 16x6.5 = +55mm and 16x7.5 = +65mm