Commenting post 487:
This blog is not a good place to discuss all these items at once, if you would post this on https://forum.freecadweb.org
I think the discussion can be much better and include other people as well.
But to give a short answer, if the IFC file contains IfcBuildingElementProxy objects, there is nothing we can do direcly, there is no way for FreeCAD to know it is in fact a window. But in FreeCAD itself any object can become any BIM object. So in this case you can take all the objects that compose your window, then Part -> Make Compound, then use the Window button to turn the compound into a window. This window will be unable to cut into a wall, though, becuase it has no way to know what shape should be used to do that. So you would need to model that subtractive shape yourself, and use it as the SubVolume property of your window. Another solution is, as you did, model the opening separately fromthe window.