Nah, I actually think you'll be fine. People have been running 18x8 +40 offsets with not much problems. If you do the caculations, the .5" you add to the outside of the rim, is more than the 5mm difference with the offset. You MIGHT have a small issue with rubbing while hitting bumps taking HARD HARD turns with the stock (soft) suspension. But other than that i think that size would be nice.
After you install the wheels you will definetly want to lower the car.
I installed a set of staggered 17's on my '02 @ stock height.
It looked like crap because of the wheel gap.
I ordered Tokico HP & H&R springs that same day.
Huge difference in looks!!