I was in Missouri yesterday and bought another sheet. Now I can redo the leftmost module (the yard) and will have plenty to use as base material for terrain experiments. (I might put a hill on the corner module with a cut for the track to pass through.)
Another variant: I add one more track on the right side of the yard, and it will be used as a home for the locomotives/switchers when they are not working. Is this better or worse than the previous plan?