I think you should go with plants only. I offered to do a build for my daughters class room. You have to relize some ppl are ignorant, and might think the Darts are poisonous. A lot of care goes into these guys. I would suggest some type of simple tree frogs, maybe just the Green ones. I would say do a 20 or 30 with a water feature if you arent putting any animals in there. If the tank is empty I think it should have something to catch the eye and a water feature will do the trick.