Here is a couple tips to add to what you find and what u already know:
Make your upper back tight, a tip that helps is to squeeze the bar.
Arch your lower back, take a deep breath and push your lower abs outward.
Right before you start a rep, lift your toes off the ground, this will help you keep the weight on your heels.
Break at your hips before your knees and dont let your knees come inward during you ascent.
I think box squatting is a great learning tool, it allows you to learn to sit back properly. Sit slowly on the box, lean back a little, and come straight up. Eventually you will learn to sit back into the box and then you will have it.
Your squat stance width will come to u, play with it... and in a couple years you will find what is best for you with heavy weights.