Great tank plan !
For the background - if its going to be against a wall which I presume it is, get some heavy duty cardboard backing; Artists mounting boards are great. Cut to size and stick together as necessary. Very easy, very changeable, very effective.
The only other question I would have is whether you are wedded to that substrate ? The malawis really pop with natural sand or gravel, or black sand. Those bright substrates can really wash them out a bit.
For the background - if its going to be against a wall which I presume it is, get some heavy duty cardboard backing; Artists mounting boards are great. Cut to size and stick together as necessary. Very easy, very changeable, very effective.
The only other question I would have is whether you are wedded to that substrate ? The malawis really pop with natural sand or gravel, or black sand. Those bright substrates can really wash them out a bit.