Sorry guys - a tank like this has no business being stocked with monster predators. As it's on display for his customers, it needs to be pristine. Monsters will make a mess of that tank in a hurry, and since it's viewed from all 4 (8?) sides, there is no hiding it.
I see a freshwater plant tank as being the best choice for this setup, by far. Maintenance can be reasonable, you can stock it with a variety of active vibrant colored fish, and the aquascape can be jaw dropping if done right. Check out
Oliver Knott's website for a few ideas.