Three people (minimum) on a Kick-Off Call: 1) You as ASC, 2) Streamline Writer (either Developmental Editor or Ghostwriter), and 3) the Streamline Author!
To get a glimpse of Streamline ASC, Nathan Sahly, leading a Kick-Off Call, please see the first 5-10 minutes of THIS video link.
See below for an example of a Kick-Off Call Agenda: