First off if you are going to do this you will need a very large tank! Secondly I dont think that having more than one of the same species will work in the long run. Maybe if you had different species, like a Diodon holacanthus, Diondon hystris, Chilomycterus shoepfri, etc..... From my experiences puffers of the same species dont get along all that well......but different species are better, but there are always exceptions. Why not a porc and a couple Arothrons?