forget holey rock. the sharp edges will ruin the fronts eyes. Get some rounded boulder type rocks for them to hang out near. this tank is WAY too small for 5 fronts. Also be aware that having calvus and comps can result in cross breeding, so take your pick. Julies are agressive, and will guard any rock pile to the death. Anything small enough to fit in a fronts mouth WILL get eaten. Fronts do better in a species tank. You will need an absolute minimum 6 ft tank for fronts.
Forget tropheus if you have these fish. Tropheus are notorious for getting bloat, and must be kept on a strict veggie diet. fronts will tear a whole shrimp out of your hand.