You don't need to change a thing about your back angle on your ascent. Except for your position at the very top, those are wonderful, hip-driven low bar squats. Keep doing that. With that said, you do have a couple of problems with your start position. Your knees are bent at the top and you are leaning over at the hips a little too much at the top. You want to stand up as normally as possible. Knees should be fully extended and hips nearly so. You are overdoing the look down cue, too. Remember, we want as normal of a standing position as possible. You are jacking your elbows up too high, which is probably what is hurting your arms. The head down, round upper back, overextended shoulder (elbows up too high) all go together. They often also cause pain in the arms. Some resources for you:
Preventing Elbow Pain in the Squat | Nick Delgadillo
Low Bar Position Stretch | Paul Horn
A Clarification on the Squat Grip | Mark Rippetoe
Check this stuff out. See if it helps. If you are standing up correctly and have made the various grip adjustment and still have pain, try wrapping your thumbs around the bar. This may alleviate the pain in your arms, but it can shift the stress to your wrists. You may need some wrist wraps. If none of that helps, the high bar position is the next stop.