Sika,
I didn't see you warm up sets, so I don't know how narrow your stance was on those. From the back view though, I see a squat that could benefit from just a little bit narrower stance. It'll give you just a bit more oomph for keeping the knees out. With that said, you are a taller guy and you do manage to get depth with this stance. I'd experiment with finding middle ground between this stance and what you called a 'too narrow' warm up stance.
Is your wide grip related to the upper arm issue? You could get a bit of a tighter upper back with a slightly narrower grip, but only if it's feasible with your current flexibility. You get a bit horizontal on some reps, but I think more firmly set upper back could help. At least we know you're using hip drive.
I think I can pick up on that little rotation you speak about. Make sure both knees are out hard and symmetrically - no caving on one side.