I have been using online discussions as digital Socratic Seminars. I recently wrote a short post about the advantages of online discussions. You can read it on my blog, if you are interested. It can be found HERE.
I like your idea of using online literature circles. Here are some ways that I've used discussions (I now use Moodle):
There are so many ways to use discussions.
Great idea with the vocabulary. I'm going to try that. Thank you so much for sharing.