Hi, David!
I use 2 different foods to feed my mbunas: pellets (NLS cichlid formula are very popular) and a good veggie flakes for cichlids (mine are ON brand).
For substrate, it all depends on how is your local water and what is appealing to you. If the water of your area has a pH good for mbunas (relatively high), I would use plain sand. If it's pH is somewhat low, I would use a substrate with a high pH buffer as fine crushed coral or the EC cichlid sand substrate that comes with bacteria and buffer and is now available as gravel, fine sand and crushed coral sand with brownish particles (this last one is the one I have in my tank).
Enjoy your tank and send us some pics when everything is ready.
Good luck!!!