A: You're looking at it. The definitive copy can be found within the GnuCash Guide http://www.gnucash.org/docs/guide/
A: Yes. Go to http://www.gnucash.org/cgi-bin/mailman/listinfo/gnucash-user and http://www.gnucash.org/cgi-bin/mailman/listinfo/gnucash-devel to subscibe.
A: Yes, you can search the mail list archives at http://news.gmane.org/gmane.comp.gnome.apps.gnucash.devel and http://news.gmane.org/gmane.comp.gnome.apps.gnucash.user (and http://news.gmane.org/gmane.comp.gnome.apps.gnucash.german if you speak German).
A: Yes. Many of the developers hang out on icq in the #gnucash discussion on irc.gnome.org. Also, there is a wiki online at http://gnomesupport.org/wiki/index.php/GnuCash.