Some people can use sub-folders and sub-sub-folders, as many as they like (I have about 100 folders in my downloads). But others do experience problems, especially with BV installed.
But I think the walls and floors are less likely to make trouble than for example clothes, so I think it's save to say: just try it. Make a couple of folders and put some files in them. Then start the game and if you find the walls/floors in your game, all's well.
