1. I'd suggest "Begin Step" and "End Step" events.
2. Being able to drag "Copies" to different positions in the room editor after it has already been placed.
3. (x,y) position of the mouse in the room editor.
4. Since the room can expand infinitely, it would seem easy to lose track of Copies and tiles in the room editor. A way to see what copies/tiles are in the room and being able to navigate to that said object/tile would be very helpful.