A 6 X 6 could be hinged in the middle and placed on a movable platform. When not in use it could be moved to the side of the room or placed in a closet. This feature would also allow one to get to center sections without having to cut in popups.
Hi Greatplains Railroader
First off flat ground isn't flat it sort of undulates so don't forget a few raised bits in the scenery even if its only the thickness of a couple of sheets of corrugated cardboard.
Six X six does seem a funny size but I would divide the space in half with a back scene, covering the mouse hole for the trains could get interesting if the scenery is predominantly flat
But this blocks the view of the trains allowing two totally unrelated sites that are supposedly hundreds of miles apart to be done say the big city one side and the one horse town where even the horse has left the other side
By blocking the view of the trains and the other side of the layout you gain the impression of the train going somewhere and dont loose the realism of a scene because the next one intrudes into it.
If this is the first layout keep the track plan simple and manageable and have a point to extend the layout built in, these things tend to take on a life of there own and do grow it is better to extend rather than go back to zero operations.
Until it reaches the no choice point extension is the way to go.
Regards John