I think it is unlikely that the last class be a Marauder, for the simple reason that they are the most basic troops in a Chaos army - just like state troops are for the Empire. The Chosen were Marauders themselves once, but they were favored by the …
I've always loved dwarfs in Warhammer, so they'll be my first choice . An Ironbreaker most likely... their fluff and looks are just really cool. I mean, check those guys out! uk.games-workshop.com/dwarfs/tactica-ironbreakers/images/BWIronbreakers.jpg
I've no clue what the mount could be, but so far the only "ridable animal" that was associated with Dwarfs is a pony (pulling a beer cart). In the 1st ed WFRP book there was artwork of a dwarfen army with a few boar riders, but that's quite old and …