What these later posts in this thread emphasize, is pretty basic. The wider that you can make your radii, the better your operation will look. Back a zillion years ago when I first got interested in zero scale, I read (probably in the late "O Scale News 48/ft") that 72 inch minimum radius was the de facto (actual) number that ANY model engine could handle. Simply stated, that meant any loco you might purchase would be able to navigate 72 inch or larger radii. That's a thought that is NOT trotted out often enough these days. Soooooooooooo unless you have a bit over 12 feet of space.............
Simon
Regarding Mr.McCabe's post below, I neglected to say, the LARGER you can go the better!
Thanks Frank!