I was listening in on people talking about visits to young church plants. A common reflection was the tendency for the new church plant to feel all wrong. It feels like a bunch of people who don't really know each other thrown into a room and told to get on.
This is one of the weaknesses of the otherwise pretty safe 'hive off' model. You end up with a motley crew of eager Christians but no church vibe or identity. It would seem then that one of the most important things for a hive off plant to focus on would be forging their identity.
This problem can be avoided if the church plant is made up of a deliberately selected team. Such a plan has more of a group feel from the beginning.