Hey Joe
The set of 300 looks better with less plate spin. The hips and knees should break at the same time. You're holding the knees back a bit when you start so they're getting into position late.
Bring your stance in a little so your heels are under your shoulders. This looks a bit wide. Then keep your knees pinned out as you drive the hips out of the hole. The hips should go up rather than back.
As far as the grip, does that bar have a center knurl on it? It may help to get a bar with a center knurl or at least put a small piece of athletic tape around the middle to keep it from sliding around.
Start with a wider grip so you can make sure the bar is down low enough on your back, then walk your hands in closer to your shoulders. If you start too narrow, the bar will not get low enough. Watch this video from Nick D and make sure you're in the right spot.