knights encarmine i would suggest wissenland, particulary nuln, as they are a group of arrogant nobles(albeit deadly) who you find in the courts of nuln.
for nordland there could be the Sons of Manaan
Hochland i remember reading of the knights of the silver mountain, who often come to the aid of hochland.
ostland: von raukov's nephew is grandmaster of the Knights of the Bull, an order based solely in ostland.
for secondary weapons: yeah it's in the model file, but you would have to edit the textures so that the model will have textures for a hammer instead of a sword.
I had a script going for my earlier work for when one of the new grandmasters i created died(default empire model, with bodyguards using same models as respective knightly orders) a new one would show up like the reikmarshall script.
On the middenheim- Talabheim thing I read that Knight Panthers have a headquarters in middenheim as they are used as todbringer's bodyguard. As on of the Lectors of ulric dwells in talabheim(second largest city for the ulric cult) there is a significant presence of white wolves in talabheim. But it is dwarfed by the knight panthers there, as white wolves are dominant in middenhem, the panther is dominant in talabheim.
Kind of rambling so here is one more thing: Hunters of Sigmar: a knightly order founded during the storm of chaos, they sound like they act like armored rangers but there equipment is dirty and dented from many battles. they only operate in the Drakwald so maybe an aor for factions who have provinces in drakwald?
ok im done lol
edit: ok maybe not here is a good site on the knightly orders and pretty much all things empire:
http://www.warhammer-empire.com/library/