Usually the basic skate hollow for a goalie is 7/8, some go 3/4, but I heard from my goalie coach that 1/2inch is good and thats what i use. It gives you enough edge and sharpness to dig into the ice for sliding, while not too sharp to wher you cant shuffle.
As for the butterfly slides, you want to push off with the toe of your skate. Preferably the sharp edge on the front of your skate, dig that into the ice and push off it, once your push is complete, re-posotion your legs to close the 5-hole, and you should be able to get a good wall-up butterfly slide fide to side.
Also, a good drill for this is start in a stand up position, butterfly slide to the left, stop yourself with your outside(left) foot and instead of coming up, immediately push yourself back to the right, then stop on the outside leg(this time the Right leg) and push to the left, complete this a few times, and the butterfly slides will be a piece of cake