Welcome to Tropical Fish Keeping.
First, what are your water parameters (pH and hardness)? The first key to compatible fish are fish that share reasonably identical water parameters, plus environmental things like plants, rocks, wood, caves, swimming and/or growing space, etc. Then comes the behaviour/temperament of the fish themselves.
You have a 170L/45g tank. The Ctenopoma acutirostre
will attain 6-8 inches so it is fine in your aquarium. But although it is somewhat shy as a species, it is nevertheless a predator and will eat anything it can fit in its mouth. So tankmates need to be large enough. Gourami should be fine; Congo tetras are possible, though they are shoaling fish and need to be in a group, say 5 minimum, which would work with just the Leopard Bushfish and a bottom fish or two if small species (some grow to over a foot, not suitable). Or one of the medium-size barb species (also shoaling fish). Or a pair of African Butterfly fish (Pantodon buchholzi) for the surface. All of these fish prefer dim waters, so floating plants would be good.
Knifefish I would not recommend for a 45g. The black ghost knifefish from SA attains 20-24 inches and requires at least a 200g tank--one must recognize the potential and prepare for it if the fish is to be healthy and long-lived. If you had the space, this could be an interesting setup, a group of rather odd fish (Pantodon, Ctenopoma and one knifefish) but this needs a spacious tank. The knifefish is also predatory, and more demanding concerning water conditions (soft, acidic water and very stable to prevent disease).