I have the same sized wheels on '12 WRX also.
I picked 245/40R18 over 255 or 265/35R18's for better DDing. I notice the tramlining, more vague steering feel and decreased turn with the wider tires. I don't track or drag.
You'll need to roll the rears. No spacers needed for our calipers.
As for the brand of tire and where to purchase, Tirerack is a good place to start.