Jan, I did follow GRJ's adventures, I may need a few hundred more C clamps and Tom Tee . Seriously, that overhang is a good idea to moderate the 45 degree clips.
I plan to call Mianne tomorrow and use Dave's plan view, along with several questions raised here to see if we can nail this down. This exercise has produced a lot more surface than I thought I would get. A decent switchyard and the round table appear to be feasible per Stangtrains plans in OG railroadingrun 299. Plus I have space for boxes (sorry, I do save them) and other stuff.
Many thanks to all for the comments and I will let you know what feedback I receive.