Simply limiting size, throttling invites, and ejecting troublemakers, goes a long ways to civility.
I'd cultivated a surprisingly good, small (~40-50) member community on G+ at one point, largely on that basis.
Mutual anonymity (myself as founder and moderator) worked. It wasn't conflict-free, but conflict resolved, quickly. Most often problems removed themselves, rarely (2-3x?) they had to be removed. That was done as quietly and civily as possibly.
I'd cultivated a surprisingly good, small (~40-50) member community on G+ at one point, largely on that basis.
Mutual anonymity (myself as founder and moderator) worked. It wasn't conflict-free, but conflict resolved, quickly. Most often problems removed themselves, rarely (2-3x?) they had to be removed. That was done as quietly and civily as possibly.