He does have auto changes. By "be better about holding your line into the corner to prevent the change until you change the bend" do you mean maintaining a straight line away from fences instead of drifting in order to get the lead change?
As far as youir pace; it's pretty typical for riders to be tentative to the first fence and then build pace as the course progresses. A very simple way to distinguish your trip and move up in the class is to really march up and attack the first fence. You can always back down a notch if you're a little strong or deep to the first fence; but this leaves a stronger impression in the judge's mind than the typical tentative first fence.
I really like your horse, and he seems like he has some show ring miles on him, so if you learn to recognize his best pace, you won't need to worry about your eye for distance, he'll take care of that for you.
When schooling (and showing if you're calm enough to think about it) any time you get a less than ideal distance, ask yourself what pace created the distance - too much? Too little? And try to make an adjustment before the next line. On your opening hunter circle, concentrate on how your horse feels, ask yourself if this feels like the lick that makes the distances happen automatically. Once this clicks, I think you're capable of laying down some really nice trips, it's almost there.
I watched the vid again, and as far as your eq, I agree - you can stretch down a little more into your heel and you do have a bit of a hunch or roach in your shoulders. I think this is connected with the low hands - if you pick your shoulders up and back, you'll also get more bend in your elbow and your hands will likely come up.
The best way to fix subtle, tenacious position problems is to watch a LOT of video; and if possible, to watch the video ASAP after your trip so you can remember exactly what you were doing and what it felt like.
I really do like your horse, he can come live in my barn anytime, and your turnout is lovely - you make a wonderful first impression coming into the ring.
Good luck, and I'd love to see more videos as your show season progresses.