I can select and deselect sectors and individual planes in the sector. I made controls for changing height and texture offsets universal, and this helped me to realize that the texture offsets for the floors were not being taken into the calculation, which I immediately fixed.

The only things left are: add/delete sectors, add/split/delete planes, select by box, then I need to connect the map view and selection code to the 3D render, so that I can also perform all this editing in that window as well. Then I can add the lighting window, and work on making sure everything up until this point works flawlessly before moving onto moving geometry.