What information do you need about foregrounds? You will have to be more specific.
As for upside-down ledges, if you want to place object 58 (ceiling of ledge) then that's tileset-specific so you will need to ensure that you choose a tileset that works with that object. The easiest way is probably to look at which sublevels already have that object and use their tileset.
Cave 0, Forest 1, Snow, Grass 1, and Cave 2 should work best with that object.