No, do not put more than one male in a tank. Betta's really do best in tanks around the 5-10 gallon mark IMO. A lot of people may disagree but it is my belief Betta's do not enjoy big tank due to them being so deep, unlike the places they originate. A Betta may do alright in this tank but it would really limit potential stocking, IMO it would be best to try and get a smaller (Not too small!!) tank where the Betta can live on his own.-