Can, what is the std tire size? Change to lower profile to maintain similar overall rolling diameter.
Lowering the car also can use sport/lowering springs.

You mean 235/55/R18? That one is too big. The best size is 235/50/R18 which is closest to your std overall diameter. The other option is 255/45/R18 but I think will be too wide for your car and makes it too heavy.

As for suspension, I've never used GAB before so cannot comment on that. I've only used Eibach, Tanabe, and APEX and I can say they're all good with Tanabe NF series being my most preferred one since it's the most comfortable. Not sure though if have for your car.