tetras or rasboras,

I'd start with 20, keep the water low and grow from there, you could always add tons more later. it'd be fun to see a tiny school in a monster tank like that for awhile, before you go all out. I'd also consider keeping the aquascape fairly adjustable so you could experiment with schooling patterns.

but if you're gonna do cichlids. I'd start with monsters that are popular like oscars, green terrors, or frontosas. I'd love to see how big any of these would get in a tank like that.

as they're growing, you could always research for more appropriate cichlids to add later, but it's also appealing to keep it just one species.

oscars and green terrors are south american, and frontosas are tanganyikan, I do wonder what the malawi equivalent is to these fish, cause that's an interesting lake of fish too.