Yes, a user will create a group. They should either be by invitation only, or require permission from another group member/admin to join. (do we want to bother with admins for the MVP?)
An expiration date is a good idea--maybe send a warning after a year of inactivity that it will be deleted in 90 days if no further activity or something? --I'm not sure this should be a part of the MVP though.
Do we want to do only geo location or enter address, or both?
Group object?