I am far from an aquascaping expert, but I suggest a "driftwood" assembly near the center of the tank, surrounded by an HC lawn, with something like Rotala green mingled in with the driftwood. You could start this by using the dry start method - growing the HC emersed, then adding water later. And, from my experience, Flourite black sand is a great substrate to do this with, unless you want to go with ADA Aquasoil.