The German riding pyramid goes like this:
Rhythm, relaxation, connection, impulsion, straightness, collection
This isn't meant to be rude, but I don't think you're asking for collection, rather connection.
Leg to hand not hand to leg. Push your horse to the bit, don't pull him back to it. In all the pictures except the one or two, he isn't tracking up with his hind legs, so I would say increase lower leg and lift hands slightly.
Now with that being said I love that you have pictures of him stretching over his back! It causes me to assume you are releasing properly, and searching for the bit when you drop him to the buckle. And, if this is something he is starting he doesn't have muscles to maintain so allowing him to come out of the contact/frame is totally ok!
The last thing I would say is that I would work on bringing your leg back, and more underneath you.
You're off to an awesome start and look like a great rider, I would love to hear your thoughts even if it's a disagreement :)