It doesn't seem as though anyone has answered your question about lowering the car. Yes, go ahead and lower the car. It will make the 18's fit within the wheel well better and the car will look a lot better. Put on some Tein CS's and you will be able to adjust the height to exactly what you want. You could be lower in the summer with the 18's and then crank it up for the winter. I don't think lowering it will cause you any issues during the winter driving. But of course I live in Texas so I don't worry about snow .

 

I have the exact same GS. I have to give a . They look YLGU. Just my opinion.

 

Thanks for answering my question about lowering.