Well, swapping wheels and tires won't affect your alignment, I'd get it done with your stock wheels, may prevent damage to the 18s.

I have the 712's in the same size. They are a good tire for the money. I have 25K on mine, they are starting to get loud now, I'll replace soon. But for the money, they are great. Check out www.tirerack.com reviews, they beat out a lot of more expensive tires.