I'm sorry for no further replies. Since the Xubuntu team – myself
included – is volunteers only, other life (like summer) sometimes
gets in the way. I've sent this reply to the development mailing
list, where other people can assist you too; please keep the list as
a recipient in your replies.
The flyer is in the need of an update; if not visual, at least some
content could be refreshed. Would this be something you would be
interested to work on?
As for "proper roles", Xubuntu works like a meritocracy; once you
have committed enough meaningful (and sustained) contributions, you
can become a member of a subteam, then the Xubuntu team. After
joining the Xubuntu team you can become a team lead. This process is
described in more detail in the Xubuntu Strategy Document, under the
section "Community" (look for the heading "Xubuntu Team") .