Adding a counselor, coach, and other District or School staff to collaborate with you in the same classroom is as easy as adding another teacher. They would have the same functions as you. They can post Announcements, create events, organize Parent-Teacher Conferences, send messages, and many others.
Alternatively, they can also create their own class. They can select Other under grade level and this would allow them to not specify a grade level.
More information and steps to follow on how to create a class can be found here.
Please note that in the basic ClassTag plan, teachers can be part of up to 7 classrooms. You can learn more about upgrading to ClassTag Connect here specifically designed for schools and districts.