If they're in a cycled healthy tank, I wouldn't worry about it. They need a few days to adjust, not only to the water and tank decor and lighting, but everything swimming above them, and on top of the food and feeding schedule. They need to figure out it's completely safe to make the 'air run' whenever they want rather then having to carefully plan it out. Typically they will spend a lot of time 'looking up', then make these elaborate maneuvers to work their way to the top of the tank, later they just will go straight up whenever and wherever they feel like it. On top of that, are also usually more active at night. Its also impossible to know the 'social structure' they had before they were lifted from the store's tank (it's hard to tell what the heck they think of each other even after months together, one may of just been added at the store before you got him). They also aren't the brightest fish, so don't expect too much behavior that makes any sort of sense at any given time...
In a 55, I'd go with 5-6 of them at least, they'll be a lot more active. And if they have different 'sizes' of the same species at the LFS, try to mix em up as much as possible rather then match them all up.
They are also the easiest fish to add to a 'school' with no worries of aggression or acceptance. After freaking out in the bag acclimating, they go straight to the bottom and its WASSSSSUPPPPPP to the others.