Pendlay's and Rip's approaches to the power clean differ, especially at the start. The idea that you need to start the pull with as vertical a back position as possible is a very popular idea in Olympic weightlifting. You'll need to decide who you want to listen to.
I would tell you that you don't need to lower the hips at all since I agree with Rip's positioning ideas for the O-Lifts. I start my cleans in the same position as a deadlift. Your starting position looks okay to me. Oly coaches would tell you I am wrong.
You are throwing your head back very violently and I predict this will cause you pain if you continue to do it. It causes you to jump backwards instead of up. You are landing in rather wide position. At 55 kg, you should break this habit early. It will not get easier to land in a more narrow stance as the weights go up. Practice moving your feet from a jumping position to a receiving position without weight as fast as you can. Add a barbell into the picture and see if you can do the same with the weight.