Looks great! For a background, I would just do a black background with paper, also a suggestion, since its a sorority I would look around for deals on fake plants and even real ones, and plant is a little more!
I would suggest a rock wall background, as I think they always look nice and natural. Alternatively, a heavily planted river scene can add a lot of depth.
I am a massive fan of heavily decorated/planted tanks, so I would move the castle bridge thing to the middle and make it a focal point, and pack out the sides and backgrounds with lots of silk or live plants. Varying heights, with shorter at the front and taller at the back, always look good and add depth.
In My Opinion your tank looks quite bare. I really love the look of moderately-heavily planted tanks and drool over almost every one I see. I would recommend a bit more plants. You cold easily start out with a clump of hornwort, or java moss. And they will spread quickly
As for backrounds I would recommend either a natural rock backround as these are very attractive and look stunning. But 3-D backrounds also minimize the swimming space which lowers the stocking potential. Or maybe a black backround to contrast the bright colored fish and plants.
As for stocking. You stocking has virtually no flaws. The only recommendation that I have is to purchase about 3 more spotted cories so they feel more secure. And will be much more interesting to watch.