I would start by adding 3-4 more pictus. they are a shoaling species that can be really cool kept this way. It would make for a really active bottom. I would then likely do a pair of sevs or chocolates and maybe some larger tetras or deep bodied siver hatchets.
add a few more pictus cats. as stated schooling fish. Then a add a center piece or pair. Maybe a pair of firemouths as they dont mess with my pictus. Heck my Oscar doesnt mess with my pictus but he is only 2.5" max.