I see a couple of things that could help you.
1. When you're pulling off the ground, ensure to love your knees back. The bar should start to travel back the moment it leaves the ground. You can work on pulls exclusively or combine pulls with lifts. You can also work on RDLs and good morning to help you gain some of that flexibility. Ensure you keep a tight back throughout the movements.
2. In your hang position, your knees are too far forward for the height you're starting our at. If you're going to work from the mid-thigh, think two-inch break at the knees, then trying to send those hips back as far as possible. You want to feel those hamstrings lengthening and getting ready to contract hard. You'll get that Feeling when you're doing RDLs and good mornings as well.
3. You're actual pulling under the bar is pretty good and fast -- nice work! I'd anything there, work on keeping the bar over your mid-foot. In that video, you look a little forward; with heavier weight, you won't be able to receive the bar properly. Think of sweeping the bar into you; that is, don't prematurely initiate your second pull. Make sure you sweep the bar as far back as possible before you send your knees forward to explode through your second pull. Youll notice you're a little more balanced and that the weight will feel even lighter.
4. Ankle and thoracic (back) flexibility need some work. Work on some mobility drills to help alleviate that. You can place a bar or weight onto to the top of your knee as your squatting to help your ankle flexibility. Likewise. Rolling out on a foam roller or PVC pipe will help your back issue. You want to be more vertical in your overhead squat position.
I hope that helps!
Javier A. Sanjuan
Olympus Barbell Club
Dear God, please help me lift heavy and be awesome. Thanks. Amen.