Comparing african species compatibility

[lanky_bark]

I'm setting up a 180-liter tank, roughly 90 x 40 x 50 cm, and I'm leaning towards an African-themed setup.
I've been researching this potential stocking list - would it work in a tank this size, considering both bioload and compatibility?
I'm thinking 8-10 upside-down catfish, syno nigriventris, 4-6 African butterfly cichlids, A thomasi, and a single African butterfly fish, pantodon buchholzi.

In terms of substrate, would sand or gravel be more suitable for these fish? What about the tank layout - any specific recommendations?
When it comes to introducing the fish, would it be better to add them all at once after the tank has cycled, or introduce them in species groups or one at a time?

[Eclipse4]

I'd definitely recommend using sand for this setup. The number of upside down catfish seems a bit excessive to me, I think you could easily get away with 4-6. They do put a fair amount of bioload on the tank, so it's worth cutting back on that. As for the butterfly cichlids and the pantodon buchholzi, I think 6 of the former and the single latter would be a good combination.