Your choice on pygmy or habrosus.
All at once pros:
fish feel much more secure having the shoal they need, less stress therefore reduced chance of succumbing to illnesses. Shoal establishes hierarchy quicker and this process only happens once which is easier on the fish.
All at once cons:
possibly slightly more chance of ammonia spike in an uncycled tank. "Possibly" as secure fish in a shoal may produce less ammonia than stressed fish without a shoal.
I would never recommend adding fish to an uncycled tank.