J, a few issues I see:
(1) It still looks too low. 97% of the time we see real trains from the side.. Personally, I'd have the bench at about collar bone height (+-)..Looking down at them hinders realism (if this is any value to you)..It also makes getting under it to do wiring/other, way easier; especially if you leave a small armless rolling office chair to plop down in.
(2) If you are not going to move soon, think about making access holes in the middle of the ply large enough to stand in for rescuing trains, building scenery/fixing track...You can still keep the sawed out piece in the hole and sceniced, along with a way to open/remove it when needed (of which there are many ways to do this). Otherwise reaching across 3' is tedious and your arms or shirt sleeves can damage structures/other ..
(3) For fear of sounding discouraging, it's doubtable you'll be able to chop it up into an around the walls layout later. The track especially will be quite tough to keep in its same pattern when exploded out to the new walls..Unforeseen things crop up..
You are a very good carpenter, though...That's job 1....