There is only one video up right now. The pull looks really good to me. Yes, your hips could be a little lower so that you use your quads a little more and your back a little less, but it doesn’t look like it would be a huge change to me. Your second question kind of hits the nail on the head - it should be a combination of pushing and pulling. Your quads should be largely responsible for moving the weight off the ground, and as it rises your posterior chain takes over more and more. If your hips are too low and you squat the weight up, you are missing out on using some of the strongest muscles in your body, but if your hips are too high than as the weight gets heavier you are going to use your back more and more and “stiff leg” the weight, as you said, which is inefficient and will make you injury prone.
Also, something that might help a little - unless you are an oly lifter, I wouldn’t pull with oly shoes on. I would suggest you pull barefoot, and star with the bar a tiny bit further from your shins (like a half inch), so that you have to bring your shins just a tiny bit more forward in order to be contacting the bar. I think those two change will allow you to use your quads better at the beginning, and then if you keep pushing through your heels you will transition to using your posterior chain.
Again, I can only see the first video, and overall it looks really great. These are just some ideas. Hope that helps.