- Looks to me like you're a bit shy in depth for a few reps (reps 1 and 2 of the second video... reps 4 and onwards, you're hitting a much better depth).
- It's a bit far for me to say with confidence, but I didn't see much of a butt wink, if any. Your lower back looks very stable. Again, don't take the video so far though hehe.
- The best angle to judge everything is 45 degrees between back and side. You can judge butt wink and depth really well from there. Consider using it from now on. It's the angle of choice for coach Rippetoe.
As far as the plates are concerned, there's a few things you can try. First, you could widen your stance slightly. This will allow you to sit more in-between your feet, so you'll be able to stay balanced without needing so much dorsiflexion. That's a geeky way of explaining but try it out.
Another option is switching to the Low-bar Back Squat. Truth is, if you want to be hitting good depth, with correct back position, as a tall athlete, with the High Bar position... then you might need need Olympic shoes, or work big time on your ankle mobility so your knees can go well past your toes.
The Low-bar squat is far more forgiving and not as technically demanding. Maybe try it out. You might like it.
Just my 2 cents