It is very simple:
1) Move the Listserve user list over - 400 users is nothing - get the master list
and do invites. If 20 did 20 invites - done. Those that can type faster, have at it.
2) Everyone who wants to be an Admin can, forums all over the internet function
3) Those who have Google Groups (reg or enterprise for edu) enabled in their
domain will have amazing functionality for sharing with the Group.
4) Profit - Congratulations, you have evolved to the next level. Use the time
saved to slowly get a cup of coffee or soup.