What features do we want/need?
What advantages/disadvantages do these systems have?
What plugins do we want?
What tag/taxonomy categories do we want?
How many forums do we want? How should they be organized?
Are forums required?
Are forums (linked to the mailing list) required? Is a gui-web-frontend to the mailinglist a suitable substitute? See the Linux Kernel Mailing List for an example of a gui-web frontend to a mailing list.
What should the front page look like?