I've got 6 in a slightly shorter tank, but the same footprint. I have a 4' 2-bulb fixture on the 6' tank, but only use a single bulb in it. The fronts don't like bright light, as live in the deeper depths of the lake and only venture shallower near dark to feed. If you get the right bulb 1 can light them up nicely.
Also don't go nuts with too much tank decor. I've got 3 rock structures, though 1 is shorter and less significant than the other two. I also went with a few natural-looking plastic plants to break up the tank a little bit, but unlike the rockwork the fish don't get injured if they spook into/through them. I setup a cave for the dominant male off to one end, then the rest spread apart throughout the rest of the tank.