You are jumping ahead a little bit. Instead of thinking about going forward for your horse (to keep up), think about the horse's jump coming up to meet you. You want to be crouching, not leeping. This will keep you balanced over the saddle.
Your release is of appropriate length, but it's hovering in the air and your elbows are resting on the horse (part of the chain reaction to jumping ahead). The purpose of a crest release is to allow you to press your hand into the crest for stability. Being that you admitting to feeling left behind, be sure to have your hand down or in the mane. The long floating crest release is also what's causing the slight roach in your shoulders. If you drop your had 3-4 inches and bring them back just a little, your will have nice square shoulders.
As for the distances... Now that I'm eventing, I've heard trainers say there's no right distance, as long as your horse goes over easily. All horses have a jumping style. However, you need to learn to ride a consistent distance. You can't always be guessing will this be a long or short spot. If you're doing hunters, you need the sweet spot. Otherwise you'll always be out of the top ribbons. Placing poles can help teach striding and eye. I spent a long time counting strides to learn optimum striding. As you go higher, you want to hit that sweet spot or the jumps just get harder.
Your horse looks really athletic, I think you guys will do well in whatever direction you go. Start setting up before the fence for a nice jump and I imagine you will see a lot of blue.