Actually, in my experience, most movement originates in the hips. Then the legs/shoulders follow from this.
Try a little experiment next time you are out riding to see if its true. With a centered stance, try turning using your 'core', your hips and abs. Then try turning focusing just on your legs, and try turning focusing just on your upper body.
Really, the upper body/lower body thing is not that important. Its all one movement, it shouldn't be broken up. Its good to focus on specific things like shoulders and knees to see how they affect turning, but in the end, its just one body moving at adapt to snow, terrain, and equipment.
As for pedaling, i never learned that as a beginner practice, it takes a fair bit of balance to do it well. I use it for introducing light carving.