Although, their ingenuity, making a horse out of men, has gotta be straight from the real Vampire Count's playbook.
they pretty much worship the knights, which is why they are carrying around a dead dude and all his belongings into the battlefield
http://www.games-workshop.com/resources/catalog/product/600x620/99810203010_BretonnianGrailReliquae01.jpg
the peasants are the lowiest of the lowest, shitstained and treated as expendable by the nobility. All those knights in shining armor, chivalry nonsense and their fancy castles are a facade, Bretonnia is a just a somewhat exaggerated version of a typical medieval society. As always, there aren't really any actual good guys in Warhammer
Are there other human factions besides them that they might add?
Bretonnia seems to be based on French knights, and Empire (germanic holy roman empire).
Middenheim (already in the game, but not currently playable/no unique units yet) are a subfaction of the Empire that has a old-Germanic theme.
Kislev, also Empire, which is heavily inspired by Russian military.
Araby, with strong Arabian influences obviously, but they never really had their own army list iirc.
Cathay, Asia-themed, barely anything is known about them, they are located in a far-away region in the east.
Tilea, a merchant city-state modeled after Genua, employs various mercenary armies.
The Border Princes, tiny poverty-ridden settlements at the edge of the Empire ruled over mostly by local robber barons. And the Chaos barbarians/vikings in the north, of course. But Empire and Bretonnia are the main ones, only they got regular army books