How many stories is 40 meters? imo, the more the better. Further, Screw realism and I don't care if someone else makes something ugly.
How much of an overhang can you make with the cantilever trusses? imo, floating houses are cool!
How big of a building base can I make? Would it be possible to make a one big building covering a homestead? I think that would be a 50x50 square meter building base.
Just as Pwnuts said. The max height is 10 stories and yes, whatever you can fit in that area goes. Fill it up or put a tiny tent in the middle. It's your call!