1 - Go to the Documentation page, download the Plug-in tutorial and install the AdvancedEdit plug-in.
2 - Learn how to use Levels, reading the User's Guide and the Help provided in the program.
3 - This is not possible yet. You may use a different program like Sketchup...
4 - Learn how to use Doors and Windows. Models of every shape (including arches) can be imported and used as door/window, giving you cut-outs of a wall in any shape you like. Read the User's guide on how to do this.

Hans