1. Is it possible to set it up a Forum accessible to only one group rather than the entire class?
2. What are other ways for groups to be used in moodle once they have been assigned?
Jack-
it always pains me to see a post with no replies, as the community here is generally very responsive - but I suspect you need to post this on the using moodle forums where others have asked questions about using moodle. The forum where you posted this question is geared towards discussing and contributing to DOCUMENTATION of moodle.
Now if you want to READ about forums and groups, there are some great resources here for that!
d.i.