DOesn't creating a terrestrial landscape in an underwater environment seem very un-natural?
Why not replicate an actual underwater enviroment, in your tank which is an underwater enviroment?
Or set up the tank as a paludarium and have an actual waterfall, that would be really neat. Have submerged plants, terrestrial plants, and emergent plants.
Please don't make hybrid endler/guppies, and if you do, feed them to something big and nasty. It is already hard enough to find pure endlers, no reason to make it any worse.