This is always a fun thing to do: if your faction was actually a civ in a Civ game (lets say Civ 5), what would be their unique things? Lets assume they're fully established and everything.
For Highwarren, their Unique Ability would be Caretaker's Lesson: Golden Ages and We Love the King Days provide bonus science. Their Unique Building would be Jousting Lists, it replaces the Stable and gives +1 Faith for improved pastures and +15 XP for Mounted units trained in the city. Their Unique Unit would be the Rat-at-Arm Knights who replace the Knights, are stronger and aren't made obsolete by Cavalry.