User Groups

I want to be able to add a school district as a user for my membership site under a plan that is not publicly accessible. I am wondering if it would be best to have the users sign up individually and assign them to a group, or or create the district as a group, add the permissions manually. Based on these 2 options I have a few questions:
1. If I create the group first would there be a problem with multiple users logged in and commenting under the same profile?
2. On the account profile would it be possible to eliminate or set up a dummy email account?
Thanks, Ty