When we looked at the Campbell archetypes in
Star Wars for our mythology unit, we talked a lot about
reluctance and
self-doubt in the "Refusal of the Call" stage of the journey. I've had some great luck in using that as a entry point to hero stories with teenagers. With Bilbo, his reluctance and "Refusal of the Call" stage goes a long way, and even further than Luke's does in some aspects.
With all of the really cool character parallels that you've outlined, and with the awesome ideas of camaraderie in the "Brotherhood" focus, a discussion of what makes a person finally believe in him/herself might be very powerful, and lay some cool foundations for later studies of more complex heroic myth like Theseus, Odysseus, and Beowulf.
Good luck!