all young horses tend to "seesaw" butt up or down. He's in the downhill stage but will hopefully level off by the time he's full grown. I'd say his neck is a tad short, but nothing alarming. Based on the pictures it seems in most shots his hind feet are pointing outwards slightly. If this happens most of the time he may be very slightly splay footed (maybe eventually cow hocked, i dunno). If this is the case you can talk to your farrier and he can try to help correct this. I wouldn't worry about it much though, my horse is slightly cow-hocked and she's 100% fine. Other than that i have little other confo experience. I must say your guy is quite cute, and he seems like a relaxed fellow.