Get some cleto Reyes gloves I thought everyone was full of ****, but the gloves actually make you land on your front 2 otherwise it's uncomfortable, it has improved me quite a bit and improved my form, a good pair of gloves are a huge difference.
Secret is the position of the thumb, Angle in relation to the body. Most things work of it Hips, Shoulder, Elbow, Wrist. Everything as regards mechanics evolved, from us standing, the thumb is part of our balancing act, more than we think. :good.
Make your hook more compact, sounds like your throwing a hook wide. Some guys also advocate the vertical fist on hooks but somewhere along the line, I was told it wasn't a good thing to do because of potential counter opportunities so I stick with horizontal. Just took time and practice to hit it right, now I practice by getting the mechanics of the body in sync to make it snap.
Close the distance and use a left hook upstairs preferably after a left hook to the body. Use Hopkins-Delahoya, Holt-Diaz, or Tyson-Mathis for reference those are just some off the top of my head. Keep the elbow parallel with your fist. Put your waist and back into it. Takes time and practice to get the timing right. As for the knuckles question, I've had hand problems in the past because I landed the same way you did, BUT, I think if you're throwing and landing jabs, check left hook, or to the body that way you'll be fine. But powerpunches I'd personally use the first 2. Body is a lot softer than the head.
Correct, and a good way to practice getting it right is hitting the heavy bag (with controlled power) with your hands wrapped but without the gloves on. Once you get used to doing it correctly, put the gloves back on and you'll notice the improved accuracy.