@Marty_Potter I would definitely use an Organization versus a workspace. It gives you more flexibility and another hierarchy with Teams. I say this because I am working with a church and we are finally drawing volunteers (guests) into the participation. Project members as guests can do many things and Asana does have options regarding what they see. I think reading these links in the Asana Guide are helpful but others like @Alexis will certainly have some other thoughts for you.
Team Settings:
Projects
Public Projects
Private Projects