1: Very good idea.
4: You can make a button with a macro for yourself to toggle the container visibility with the second Layers Panel. I think this should be very close to fulfilling your wish.
-Containers Show “Container Name” Toggle ENTER
The issue is that Rhino will not save your column spacing in the second Layers Panel after you restart the program nor allow you to filter it independently. (or it might mess up your first Layers Panel spacing).
Unfortunately, the staff has not yet recognized the issue, but we can join forces in asking for continuous development of one of the most (if not the most) important panels in Rhino.