Colt:
I think you're off to a good start. The double outer loop idea is a good one - lets you (and/or the kids) run 2 trains at the same time easily. the figure-8 lets you turn trains around. If you can put an additional 6"-8" addition onto the one side of the loop to run O-72 that would give you more flexibility with respect to the inner loop, figure 8, and other tracks & accessories within.
What track system do you plan on using - looks like old school Lionel? I assume you already have some track and that you'll stick w/that type. I may see what I can come up with if I get the chance to mess around w/SCARM tonight.
