For the most part, I imagine that people will be needing to approach you to join your team (since, surprise surprise, all the other NPC teams will have spontaneously filled up), but if he feels like he needs specific people he's welcome to hunt them down. A reminder that as Delsin said, the team will need to be 'oversized' to be approved due to the nature of the S-Class jobs and the special nature of the tasks at hand.

For any characters without a team (or in fact a prospective team), get them to approach one of the guildmasters and they'll ensure you find your way into one of the two teams. Once the teams are sorted I'll post up the jobs that each team can choose to do, at which point we can start out on our adventures!