I'm a bit of an African riverine nutcase, some might say and the only African fish I can think of that is borderline suitable would be 6-8 Microsynodontis sp. 1. These catfish are a lovely little ~2cm SL species that will be active by day and use midwater too, providing you give them a decent cover of say a nice Anubias coffeefolia plant attached to some bogwood.
There are very few small African species that come into the hobby, the most common would be the variants of Lampeye Killifish, but there is no way I would put them in such a small tank. A 40x28x33cm tank is tiny, it can turn into a toxic soup rapidly and it gives the fish very little room to move in. In addition, some small species do exhibit nasty conspecific aggression between males, for example Sawbwa resplendens (not from Africa) and Barbus faciolatus (which is African, but reaches ~6cm SL).
One word of warning regarding African shrimp, do not buy Cameroon Fan Shrimp (Atya gambonensis) for that tank... Any babies you come across in shops turn into ~15cm specimens.