Awesome input!
I am exploring my own leg system, and it is quite energy demanding. 
I was hoping some robotic tech could create a humanoid robot (like Chappie) to
do the manual labor.(Farming, small business labor) 
I've spent a lot of time studying cats lately, what their skeleton looks like and how they move. So, I have a very good idea of why they are built the way they are and why the skeleton moves as it does. A good bit of why quadrupeds are stable on 3 legs has to do with where the center of gravity is. The weight of the head and neck brings this forward to not far behind the shoulders. A quadruped can not walk without a head extending out and shifting the CG forward. I've plotted this out on plain old graph paper!
After plotting footfall patterns for walking I found that the cat is statically stable over a good bit of 3 legged positions, it is at the extremes of the walking gate that momentum must carry through.
Bipeds are different and rely on the foot to be statically stable, it can never statically balance on 2 points. Now, take a look at Mossimo:
https://www.youtube.com/watch?v=-qrLOtgYIWsMossimo does not actually walk like a human, the legs never stretch out, and are in fact closer to the rear leg of a quadruped. Note also the large feet (which is unneeded in a quadruped). Note also how it shifts it's torso back and forward to adjust the CG.
What I am suggesting is that you plot out leg and body movements and tipping points and see what you discover. You can not build a successful biped or quadruped without the geometry being correct, the architecture has to follow the math. What happens is that most people build out of what robot parts are available and the geometry and CG gets pushed back in importance where as it should be the first concern, not the last.
With my quadruped I had a real starting point as I went from nature, and what I found is that nature does things for good reasons. We need to consider the why and learn from it.