Here are my unorthodox suggestions:
Put all the complexity, like yard throats, reversing loops, etc., into corner modules. Then connect those corners with straight parallel tracks. This way, if you ever move the layout to another space, you can reuse all of the complicated stuff and only need to adjust the straight sides.
I use 15/32-inch BC plywood supported from the floor, not the walls, with 1 1/2-inch PVC pipe legs. Each leg is connected rigedly to the plywood by a 1/4-20 eyebolt with a 1/2x2-inch bolt through the pipe and eye. I put the legs freely wherever I need support and bolt steel angles under the plywood with 1/4-20 carriage bolts wherever the span might sag. (The angles don't actually connect to the legs.) I use the space under the table for bookcases, cabinets, desk, and workbench.