He's posting in the second photo, meaning, he's rocking back and not really leaning down and into his chest. Using bait will help to correct this. Getting him to lean into his chest is would be the human equivalent of the "head up, chest out, shoulders down/shoulders back" they teach in achieving correct posture. Don't worry about his tail--you work on the tail later.
From a construction perspective, he is a bit high in the rear (caused by his fairly straight stifle) and has a low tailset. That said, it's my understanding that you're just looking to show him presently, and working on the things I've mentioned above, plus getting a bit of weight on him will help hide these things.
With that said, these issues will become noticeable again when you move him, and there's not much you can do about that, other than find a speed that best minimizes it and keep his head up while moving.
While my girl is posting a bit in this photo as well, mostly, she looks the way she should when stacked appropriately.

Hopefully this helps.