I want to do something like this in the near future. That looks amazing. Just one question: Why do you have a current maker in there? Lake Malawi doesn't really experience currents, and you already have a canister filter in there(which should provide enough aquarium circulation). I could be seeing it wrong, but the thing on the glass on the left side looks like a current/wave maker or something along those lines.
A background can also provide an effect like a rockshelf - like many of them would experience in the wild - it gives them structure and cover, and may make the fish more bold. Aesthetically, I like it cause it hides unsightly lines, but that is purely subjective.
I'm with you on the wavemaker. It keeps the water nice and circulated/oxygenated and hopefully helps move the waste to the filter.
Definitely add a black/dark coloured background, it will add depth to the tank and make the colours on your fish really pop and standout! It will also make the fish feel more secure, which will then make them colour up even more too. I would also maybe stack some more rocks higher aswell creating more little holes and caves for them to swim in and out off, make sure to keep the open swimming space for them tho. Nice tank mate