As it mentions in our profile (click the shaded name, Pearl Gourami) a pair is fine provided the female has sufficient space and places to get away from the male. Having 2 females to a male helps, since his attentions will be divided. You have space in a 55g so I would suggest one male and three females. Or two males and 3-4 females should work. Lots of plants to break the tank up, and some floating plants as gourami love to cruise among floating vegetation.