Are you doing a species only tank? You could have quite a few in there while they are small but they grow fast. Once they get into the 6-8 inch range you would have to thin them out. The one I kept was very rowdy and aggressive even to non Venustus fish.
More like a few large caves rather than rock piles. They will get pretty big for rock piles... A lot of open space with some caves to hide in once in a while.