You mentioned getting a camber kit to help with tire wear. Is that the only benefit? What might tire wear look like w/o a camber kit?I think 8.5 would be a good one to go with but I would not go any lower than a 35mm offset unless you want to get into rolling fenders and all of that. I was running a 18"X 8.5 with a 35mm offset with no issues with lowering springs.
You could probably get away with a 30mm offset with out rolling the fenders but IMO you would be close.
Wheels will change the look of the car the most but I would do springs first to get rid of the wheel gap. And also remember once you lower it you should look into getting at least a rear camber kit to help with tire wear.