Increasing the height of the props as you get further back gives somewhat of a forced perspective to help things stay in balance. If you can see thru your props, you can set up "layers" without obstructing anything.
You could also mount props on the walls, or just use "wall washers". They take up little/no yard pace and yet can have a nice effect on the display. A garage door is also a nice large, flat surface that can be used as a projection screen, or hold a grid or other non-heavy props.