OK, I'll try to be a little clearer. First, with the benchwork in the PDF picture, it doesn't look like you will have much room between the walls and the edge of the benchwork. Might just be my old eyes and "wide hips" talking, but most "experts" (term used in jest) recommend at least 24" to 36" aisle spacing.
Second, put two switches on each side of your balloon loop so that the turnout goes to the outside of the loop. Then connect the first set of switches with O84 curves and the second set with O96 curves. Now, you have two tracks to use for concealed staging of trains while the O72 mainline allows for a run-through. I specifically recommend those curves so that you can run longer equipment and engines through there with minimal chance of problems. Of course, since most, if not all, of that track will be hidden, you will have to be very careful in the track laying, and you will have to develop a system for identifying occupied tracks to avoid collisions as trains enter.
Chuck
