I have a question: If there is no available follower that you are allowed to take, are you required to start a new civilization instead? (What if there is no unoccupied continent?)
That's an interesting question. The rules aren't explicit on this point, but a strict reading of the rules would mean that you either take a follower, or you start a new civilization. If you cannot do either then you simply skip this step.
Then again, I can't imagine a scenario where you wouldn't want to take a follower or start a new civilization if you can, so it's kind of a moot point really.
I hope that answers your question!