Here is an interesting addition: a reason for the layout to have an elevated line: a connection to another railroad and a spur (at about 7" in height), all at O60 minimum diameter (with a tunnel).
This would be an interesting and fun RR to build and operate. Perhaps operate as two RRs, interchanging: the elevated green RR that descends into the valley below, making a connection with the blue RR running through the valley. With some shared tracks, or trackage rights. The minimum center-rail spacing is 5" at the tightest point.