I’m not going to spend ages going into the detail of how I would make the actual careers work, that’ll turn this post into a monster :P So instead here are some basic themes from characters and troop types already in the existing lore:
Morning Star - if you build it they will come.
Young Knights trying to prove themselves and become Knights of the Realm. Also known as arrogant, obnoxious and very posh psychopaths. Give them medium armour, lots of weapons, abilities that reflect their unhinged nature and I’m sure us players could provide the psychosis.