As modern bees make larger brood nests then beekeepers often use 2 brood boxes...particularly if using British Nationals. The 8 frame langstroth will be fine for the first season if starting with a nuc...otherwise having a second brood box, if needed, is a good idea. It won't stop swarming but may delay it....and you can use it for swarm control. Many beekeepers use 2 brood boxes for a mature colony. If adding a second brood box...it's a big cold space above a small colony, if added too early, it will make it much harder for the bees to build up.