those dimensions seem pretty perfect for a larger African ecosystem, personally I really like the idea of a bottom heavy tank with larger bits of hardscape, as sand won't suit the healthy lifespan of many plants.
africna butterfly fish would be nice as a top skimmer for this mangrove-esk tank
I feel most hardscape heavy builds with good grey/black/brown contrast would look amazing
you could go for driftwood pieces that branch upwards to an extent to make use of the large middle ground, unless you were going for a negative space powered look
if you prefer less bottom heavy and landscape centered tanks you could go for burrowing fish or fish that prefer sand I would recommend chaca chaca or pacman fish as an oddball extraordinary that would benefit from the sandy substrate
