That format looks correct, though i think week three is 1 x 5, 1 x 3, 1 x 1(or amrap) I dont have the 5-3-1 PDF front of me at the moment. I think as far as assistance work he presents a variety of options. What you are doing looks ok assuming the volume does not feel like to much. I dont know that I would add more posterior chain work what with the squatting, deadlifting, and good mornings.
Thats just my general thoughts. I think 5-3-1 is pretty flexible. For example, you could just do the main lifts and call it there if you are beat up from rolling.