Users belong to groups. You assign users to groups when you create the user. You tell the groups what the users in that group can do in the groups settings.
So, if you want 5 distinct groups, create the 5 groups, one for each region. Then assign the user(s) that can manage those groups to the group they need to be in. Then, make sure that group has the permissions you want it to have in the groups settings page (so they can only see and manage their groups, etc.).
That's all you need to do at this point, unless you want to have a "public" side of the calendar for people that don't log in. If this is the case, let me know and I will explain how to do this.