DMs are able to browse, post in and manage your forums, so just keep that in-mind and make sure you're observing the forum and module rules. It goes without saying that the DM team will respect your privacy and will not divulge any discussions that take place in your private forums, so long as they're within the rules and are respectful of other players and members.
There's really no criteria other than it should be a group that exists or has existed in-game. Activity isn't really a prerequisite but it is encouraged you use the forum space given to you
The group is easily managed through your User Control Panel settings and people can request to join or you can simply add them.
Cheers!!
