As far as adding fish to the existing stock, be sure to quarantine them ofcorse prior to introduction. But the more you add at a time, the better the outcome will be. In my past mbuna tanks, anything under 6 or 8 fish added would almost always end with them beeing picked off one by one. The fact that you stated your stock is still small is def. to your advantage. I think with fairly frequent waterchanges, your tank should be fine cycling wise due to the fact that you added all the cycled media to the tank.