If I was to sell them I would just leave the back clear. So you could add whatever you like behind it. I would also move the frame toward the front of the tank so lights could be added and hidden if desired.
It's better to just leave options open rather than picking a backdrop and lights because everyone wants something different.
I would however make the tank more wide than tall next time. Add a little more depth, roughly double the size of the dish area and include a lid. As far as lights, heaters, gravel, plants, backdrops, stock, ect that would be up to the purchaser.