If you are trying to create a collision for the set of objects, your mesh and your camera, the best way to do this is in the Blueprint for the set of objects. You should only be handling collisions for a static mesh in the mesh editor (as far as I have seen).
Check this out… I have the sample character from one of the examples and they use a Capsule Shape component as the general collision for the player. You could do the same but use your cube or whatever shape and simply move/rotate it to fit your needs. The player skeletal mesh also has collision handling, but this is separate.
Hmmm. I’m not really sure what you mean here. If you mean what I think, and that you are trying to keep your player/camera inside some boundary. Is this for the whole map? Is the boundary dynamic with the character movement?
I thought about this for a bit, and came up with what I feel is a reasonable explanation. Short answer is that you might want to start centering your meshes on the origin instead of standing them on the XY plane. Long answer and reasons why are in my answer to my own question.