I've heard about a few persons who've been able to keep clowns and Africans in the same tank- but those are definitely few and far between. Cories will not survive in an African tank.
Like Menagerie said, water parameters and behaviour/territory differences are simply too significant to keep these species together with any real degree of success.
If you're interested in bottom-dwellers that display that "pack" behaviour, look into S. petricola. These are great little Synos that come from the Rift Lakes and are every bit as entertaining as the clowns and cories are.