The 5th picture is the best representation of the position you and your horse would be best at at the beginning of your study of dressage. I would even work on having the horse lower his head even more , if possible. He's a really cute horse with a lovely stride, beautiful head and seems to have apretty willing expression, if a little bit irritated at the rein contact. That might be becaause you have just a tiny bit too much downward pull on the reins.
I know it's tempting to use a downward angle to try and get the horse to reach downward, but this often puts a harder pressure on the bars of the mouth and makes the horse resist. YOu want to really try to maintain that line of bit to elbow, even when asking for a downward reach from the horse.
Keep your hands up, thumbs on top and elbows connected to your ribcage. Your leg looks good, and you sit up pretty well. There is a wee bit toomuch forward angle to the pelvis . Drop your knee down more, lift the crown of your head up.
YOur shoulders are really fairly twisted in a lot of those photos, usually to the inside. I know all about this 'cause I have the same issue. We are trying to "help" our horse bend , but we need to stay centrally balanced over them to not interfere, especially at the canter.
The horse has potential, and so do you. Thank you for sharing and good luck in your further lessons.