It would seem to me that only members and not "anybody" should be able to post to the main (homeowners') group
Why would you wish the world to be able to post to your homeowners' group?
If someone wished to contact your homeowner's group they could write to groupname+owner@...
which is listed on the home page of each group.
Board members should also be members of the main group but as Moderators &/or owners.
They wouldn't have to receive emails except possibly Special Notices, in fact, they would most likely
utilize those for announcements and could also control and use the calendar to notify homeowners'
of dates of major interest to the homeowners.
Board members only should be members of the subgroup.
You should allow all members of the main group post without moderation which would relieve the burden of moderation.
But, essentially the Board "owns" the homeowners' message board, controls it and is responsible for its maintenance
and proper running.
Founder, Fuchs Friends ®
Founder & Executive Director, The Corneal Dystrophy Foundation