Hello! With regards to introducing buns: you should probably wait until they're old enough to be spayed (unless you want fighting and babies). When you introduce them, start by giving them supervised time in a neutral-smelling area (where your first bun hasn't been often for 20mins to a few hours per day for a few days). When they seem like they get along, you can introduce them to their living space, again supervised. If that's okay, they can start living together.