well for the first one, set the primary usergroup access to not be able to see the forum, then allow the secondary to be able to once they join.
and for 2, i dont think that is possiable just with a setting, but you could use an if statement to hide the edit button per the forum.
something along the lines of
HTML Code:
<if condition="$thread['forumid'] != X>EDIT BUTTON CODE</if>
where x is equal to your forumid
and that would be placed in the postbit or postbit-legacy template depending on what you use.