Well that sounds really nice to me. Yellow labs are such nice looking fish. You could probably fit 15 + in there.
If you want to add something to that tank, I would suggest a blue fish, like Aulonocara, Copadichromis, Protomelas, Scieanochromis. These fish are more open water and will occupy the water column above the Labidochromis. And I would suggest just one species, and do like 12 yellow labs and 6 of one of the species I suggested.