Consider thinking down the road. The RR is built. The mainline is up and running, in a flat circle.
Then the creative juices start reflowing, "how about a twice around over under mainline". Too late at that point, but not too late now.
Maybe consider revamping the basic R.O.W. to mix up the mainline. Running mainline trains over and under with up and down grades adds considerable visual interest. Especially with a dual main line.
In my experience, we all like to incorporate a variety of available sidings for potential switching operations but activity frequently boils down to running trains.
Working along the premise that when you cannot exceed the length and width, go up and down; I offer a suggestion: As you construct the benchwork, allow an unencumbered structural provision to keep twelve inches clear directly under the platform to possibly add a subway system down the road. Lionel and MTH have some real nice subway trains.
Note black painted subway level.
