Bad ideas for mixing;
Angels will be trashed, they simply aren't compatible with Africans at all.
Pictus cats and kuhli loaches don't like hard, alkaline water.
Bichers (dinosaur eels) will outgrow the tank, and eat everything that fits into their mouths as they do so.
Bala sharks are social, schooling fish, need a much larger tank than 55 gallons, and the Africans would also pound them to a pulp.
If you don't have the tank yet and want to keep Malawi cichlids, you'd be much better off starting with a 75 than a 55. Forget about mixing just about anything other than groups of other Malawi
mbuna or Victorian Hap's with the afra's, though you could probably get by with a Synodontis catfish.
If you want a 55 gallon community tank, research and choose species that are compatible and won't outgrow the tank.