When I add a new group, all the existing forums show as accessible to the new group. Is there a way to make the default permissions such that existing forums are not accessible by the new group? Otherwise I am having to go into each existing Forum individually and deselect the access permissions for the newly added group.
This is the one area where mybb is super time consuming.
What you ought to do is either:
1) Add all your usergroups first before adding forums (save some time)
or
2) Make some sort of "template" usergroup and have permissions ve inherited from there.
Regarding default permissions -- If you do it correctly, then when creating an usergroup, you should maje it inherit permissions from the closest usergroup to it; this inherits forum permissions as well as group permissions.