right-click IN LIBRARY to copy or move photos in a Collection to another collection

That already exists. Right-click on the destination-collection rather than on the selection.

After you Import to a folder, and you are culling/rating, etc - it would speed up workflow for Collection centric workflows to have a Favourites Collection capability.   All that interminable scrolling to portion the Collections sub-panel to the right point so you can drag images to it is a waste of time.  It would be like the Target Collection, on steroids.  Same capability but more 'targets'.