If you would like someone else to hold a camera to film you, they’ll have to record on their own computer, while moving their own camera, as there’s currently no way for another person to move YOUR camera.
The cube can be hidden with the F11 key. Using MixCast should automatically hid your avatar when you’re using it.
If you go to Options->Spaces, you can change the background color of the environment.
Hope that helps. Let me know if you have any other questions.