I thought about extending the connecting RR at the top of the plan, around for an oval of O-72, and going across Lionel's Lift-Out Extended Truss Bridges (with a staging track or passing track). So here is an unfinished look: 6'6" x 17':
So this will support 4 trains, with three running trading places with one on the siding over the truss bridge at the front. The middle semi-circle of track on the right is on a fill, rising from about 3" to 6" at the bridge over Granite Falls.