i have no knowledge of the trewavase or the polystigma, but the other cichlids sound like they should be okay together. i have never had catfish with my cichlids either so can't comment on that. the pleco will prob be okay though, try to pick out one that is already 3 inches or so at the store. i would just leave your gravel be, it should be easy enough for them to dig in. other cichlid experts can chime in to this thread too 