Yes, get more!
there's a behavioral study that observed "8" as a "magic" number with these fish ie various behaviors were observed in larger groupings of fish, when less than 8 fish were present, the range of behaviors dropped off - depending on your tank dimensions, they do some interesting "streaming" behavior (I've ~14 "purple" harlequins in a 90cm tank, some have an "orange" head patch, others have "gold", at times the entire fish looks dark)
Males are more brightly colored, females have a deeper body, you want both males & females present to observe display behaviour in males, males will spar (without apparent physical damage), they are entertaining spawners