If I had a tank that big, I would do that awesome idea where you carve either a rock or wood design out of styrofoam and coat it to use it as a background....It looks so real and would be amazing in that big of a tank IMO.
From my tanks, the most beatifulis one of 75 g that I use to keep only loaches ( macracantha, dario, lohachanta, striata, sidthmunki, modesta, morleti and lecontei) with a lot of plants.
i just made some slate shelters out of some tiles and silicone, add some black small gravel it looks good so far. i added a piece of driftwood today, but its still floating.