1. yes, the forums are readable by all, though some are private for posting, but not replying, so that only mods/admins can start toics in certain forums. I tested in both type of forums and got the same results, even in one the were full registered, nothing private, mod or admin.
2. no, you have to add eanh user as best I can tell. But only one group is necessary, and the group must be tied to some forum in some way. Then notifiers work for all groups. This is the best I can determine-there are a lot of variables to deal with, but I think I have it nailed down.
3. yes, Admins seem to be treated the same as other users with regard to this issue... even though I'm using 1.0.3. (Didn't test for other 1.0.3 Admin funstionality.)
4. none that I know of. I saw none in the pages served, but don't have access to the server logs.
5. good point. I was just setting up the third board and didn't need groups (yet). I simply installed the same mods for all boards. Most often I would see a board having a combination of forums that do and do not require group membership-so in that sense you wouldn't see this problem. It looks like the mod was written from tha standpoint-not checking if a forum was private to readers before continuing to validate for user notifies.
Another thing I didn't test was the effect on a user of giving them person (rather than group) access to a forum-but I expect that woudl have the same effect.
Enjoy your time off.