don't have any experience with those two specifically, but i do have a spathodus, very similar from what i can tell to the eretmodus, and i can tell you it is an awesome fish, loads of personality, very unique looking, probably one of my favorites of all time. i also have a pretty cool tropheus, and although they look similar to the petrochromis i have a feeling tropheus are probably a little more aggressive. in any case, with a large number of them you should have no troubles. i have found tanganyikans in general to be very hardy, and you will absolutely have to post pics when you have everything up and running. sorry i'm not more helpful, but i think your idea is for a tank that size is awesome. you will not be disappointed