- Does there have to be a single contact?  (to prevent conflicting information to freenode?)  Or can
  there be at least a few to make sure one is available when needed?

        No, "can be one person or several" per http://freenode.net/group_registration.shtml#groupcontact

- If there's a single contact, do they represent just en.wikipedia.org, or do they have to represent
  ALL wikimedia projects, in all languages?

        No, we can designate that one person only has authority over a subset of things.
                http://freenode.net/group_registration.shtml#groupcontact  "or to a limited set of projects or users"