how many tropheus species are you intending? Tropheus are small but very territorial, I personally have 3 lone males in my 125g long and havent had problems so far, (around 60 days) I keep them with pretty much every type of African, so as for tank mates, as long as the tank mates are larger, not too docile, and could keep them in check, there shouldnt be a problem there.
I have, a frontosa, calvus, tropheus, Mbuna, Haps, Peacocks, Vics, Kribs, a Jewel, and Synodontis
a 4 ft tank, I'm not sure if two species would work because of limited distance they could be from each other, I leave this part to someone who keeps them in groups instead of loners like myself