You can still recruit crew members even if your ship does not have enough beds for them. Get new crew when you have some extra minerals to spend on them. This will allow you to get the best possible stats for crew members when you unlock new beds for your ship. Better crew members are rarer, but you still must view their stats to determine if they are truly required for your ship. Each crew member has different stats (Pilot, Shield, Engine and so on), making them a better or worse choice for the corresponding room.