I reckon you're asking for trouble, if the crayfish can catch 'em he'll eat 'em. On the flip side a big cichlid would love a nice lobster for dinner!
Also, sorry to be picky but an african set up should be just that, remember that all those species are endemic to thier relevant lake. if you want to add some other stuff why not look at some of the nicer syno's? Multipunctatus is a good bet and doesnt get too big.