D.P.
Personally, I would not choose to fight that battle! I'd minimize my stuff ideally to fit in the smaller closet. Or move the stuff to a basement, another room, under the bed bin...
Also, can't you hear him getting up and doing this stuff (breaking hangars) if he's in the same room? I think getting up before him would solve the entire problem.
It makes me nervous that he's getting into stuff AND his sister's crib with no supervision! O. of them could get hurt. And he is little so I don't agree with the idea of "making him sit in his room on his bed with no toys only coming out to eat." Good luck!