Can i add one killifish with these fish together?

Your tank is getting pretty full as it is, but to answer your question killies wont eat any of those, are beautiful fish, and great to have as an only species, You should come join my forum http://aquariumforum.forumotion.com/ to get answers to all your fish keeping questions and lots more enjoyment from your hobby by belonging to a forum of like minded friendly people. We are all ages welcome, and actually enjoy the newer folks just as much as long time fish keepers.