I too would do this until settled. Not only will it help protect the others, and handlers, but it is also a concession that other owners can see you are making, and so showing respect for them.
Your other updates sound great, that you are actively sorting the issue.
Just an idea about the abscess...I had a pony who had a strong survival instinct. In his mind, if he showed a weakness he'd be feed for the wolves. So he would hide pain as best he could. I learned to look at him very closely as a result of this. Once he had an abscess and the only sign he showed was a slightly shortened stride. It really was hard to spot but when I felt the hoof it was warm, so I started poulticing. It must have been very sore as the amount of pus that came out was tremendous, but he wasn't limping. Yours may be another like this, especially if he is unsure of himself. He may not want to show a weakness.
I only tell you this so you don't feel bad that you didn't know about the abscess.
If I were you I would talk to the yard owner about your worries and let him or her know that you will do whatever it takes to get him settled in & safe to be around. Hopefully they will show some patience with your young horse.
