In my opinion, at 4 foot, things will start to feel fast. A lake I spent a lot of time skiing on years ago was not much more than waist deep at the turn balls. While it made the wake non existent, it made the water feel fast. Down south in warm water, you may get away with that sort of depth, but not in MT (a lake that freezes over in winter isnt right IMO, and far too cold a place to WATER ski). 5-7 foot is ideal depth I think.
Without knowing a thing about MT wind and weather (other than its cold) here is my 2c... I am certainly no expert on wind, but when building a wall of trees and berm to shelter from prevailing wind, it can make it worse where you dont want it to be - on the lake itself. A good analogy is an aircraft wing. It accelerates over one side of the wing to create lift. With a straight wall of trees and dirt, this MAY act like a wing and result in the wind flowing back down over the trees onto lake faster and harder than the actual wind speed in the first place. I believe you want to disrupt the flow. The berm and trees approach works well most of the time if tall enough, however I would add Another row of spaced out trees 30-50 yards or so behind the lake to help disrupt and slow the flow of wind before it hits the berm and lakeside trees to help it flow over the lake.
Hope this makes sense.