@Dorin thanks for testing. Here are some screenshots where you can see how it works.

to 1.
Even when the base plan is locked it is possible to edit and move polylines and text.


to 2.
Inside the level settings there is a checkbox "Locked" now. If checked then this level is locked.


to 3.
I use different levels for the 3D furniture and the 2D symbols. All objects inside a level will be always drawn over the other objects. This is independent from the objects z-position.