As I thought, you don't use your leg drive, since your hips are almost at the same level of your shoulder when the bar starts leaving the floor.
Also, I'm ok with the lower back slightly rounding on heavy sets (it's "power"-lifting, not "aesthetic"-lifting), but it looks a bit too much for a submaximal training set.
My advice is to work A LOT on your set up, lowering a bit your hips and really trying to arch your lower back. Do all you can to raise hips and shoulder at the same rate until the bar clears the knees; you'll feel it in your hams more than ever.
As far as sets, reps and #, I personally like very much singles at about 85-90% and triples at 70-75%, 6 to 10 sets, a couple of times a week. Start on the lower range, adding lbs and/or sets only when technique gets more solid.
DISCLAIMER: I'm not a very strong guy (465@167), so this are just my two cents.