I have looked and looked, and cant find anything on the (06)WRX.
I want to install a set of 18 X 8.5 wheels what off set and tire size should I go with?
Any info on this wil be greatly appreciated !

Same offset at tire width as you would a 17x8.5.

Something Around a 48 to 45 offset and 245 or so tires would be OK with a bit of fender rolling maybe needed.