Kenyi, more appropriately known as Lombardoi, will grow fairly quickly and reach a size of about 5" max. They will most certainly outgrow your tank, and sooner then you may like. They are extremely aggressive cichlids and in a tank that size you will end up with just one remaining eventually. 55 gallons is the minimum tank size I would recommend for these guys, and even in that tank you will only be able to get away with one male.
Yes, I understand they are doing fine now, but aggression when they are mature is a completely different story. Have you read the pinned mbuna post?
Pleco's are generally not a problem, but there are no guarantees with these cichlids. I'm, a little concerned about a 7 inch, still growing pleco in a 20 gallon tank though.