I am following your posts with great interest. This will be most exciting if you can pull it off. You may have already accounted for this, but if your turnouts lie near the base of a grade, you are in for a lot of trouble. The lateral pull and gradient is a very effective derailer; I learned that the hard way, too. In the model train layout, we are lucky to have, here in El Paso, was built in 1986 and has two duck unders: one you have to bend in a deep bow, the other can only be traversed on hand and knee. In 1986 it was a nuisance to bend and crawl, in our present age it has become debilitating to many of the members. Hmmm, your space predicament is highly common to many of us. It certainly sounds you have thought this through, but my own experience is that trying to wedge too much into too little to be he railroad to Hell. Perhaps you will succeed where I have fallen flat on my face. Always remember: "what doesn't kill you, leaves you in jagged little pieces." Just for the sake of the conversation regarding space, I also dabble in British OO. For one thing, a lot of freight cars, and some 19th century style coaches, have but two axles. That was fine, until I got interested in later coaches with double bogies. That, in golfing parlance, became a double bogie, and I was forced to rethink and rebuild. Presently, my interests have taken me down the road of building micro layouts, the current project being 40 inches by 32 inches, just to see how much I could do scenery wise to project a broader image. That, and it is small enough to stuff into my hatchback with an eye to taking to the occasional model rail exhibit.