The lesson you should look at is ‘Defining a field as a list of things’. In the lesson it’s about ‘shopping items’, but it could very well be a user, and then you define a field on the user type which is ‘Followers’ and is of type ‘List of users’.
For admin, you should look at this post Best way to handle admin features. Basically create a field admin yes/no on the user, and use some conditions on the workflows.