50 gallons is going to be pretty small for most turtles and most cichlids, and turtles do not generally mix well with fish, and rather tend to eat them.
Perhaps you should consider something with a faux rock wall in back, bromeliads, Platycerium, Tillandsia, orchids, etc....and some small fish, small shrimp, perhaps a couple of newts, 2 small arboreal geckos, and perhaps a couple of treefrogs or something along that line. You could incorporate an artificial rain system or fogger, and perhaps a small waterfall feature.