this sounds very kewl. its a nice way to also help bring new folks into the fold as they can see that just putting a force together and trying to win a game isnt all there is to this hobby. it will be alot of work.
possibly:
overall title - army histories & backgrounds
sub titles - each army, ie. chapters/legions & race
(divergent chapters go first under thier mother chapter then if is a numerous chapter gets its own sub-sub title)
also maybe have a stickied topic at the top of the section that has links and/or other references for newer folks to use to help them create thier backgrounds. its nice to say here put your stuff here but some folks dont always know where to go for inspiration or guidelines on what would actually fit for the army. ie chaos worshiping the laughing god.....
maybe give some guidence on what general areas that it would be good to atleast minimally cover (homeworld, general theme/organization, founding/key army characters, etc.)
thanks
grip