its early days- he could just be a bit confused ie slight differences between your aids and the previous owners aids. I just wonder if this might help. Pretty basic stuff, but this worked for me when it was suggested for a similar problem I had with a mare. Slightly lift the rein on the side you are coming into ie dropped shoulder side. And I would do general schooling of serpentines and large rectangles with a counterclockwise circle at each corner, big and slow, not tight and sharp. And I would keep my hands lightcontact, so for turns I would keep inside rein steady, just slightly lifted, and give with outside rein. For stops I would just use my seat to stop, not really rely on my hands, just maybe a couple of half halt finger tweeks, and deepen your seat for halt. Are you giving him vocal aids as well? It might work for some of your problems; it just sounds like he is generally unbalanced and clumsy / abrupt in his actions.