1. Please use the multiple levels feature available in the new version 3.4

2. You can make holes in walls with large Service hatch objects 

3. I don't think that will happen anytime soon. Just import other models if the default ones are not enough

4. If you want more staicase models, feel free to contribute. The drawing in the plan can be done with this trick that I might include in a coming version

5. I don't understand why the divider isn't enough for you

6. Maybe one day, the toolbar will be customizable, but it's an expensive feature which doesn't bring that much benefit

7. Look in the modification pane of the 3D view