As in IronDM(tm), Ingredients are mandatory. Unlike IronDM(tm), IronNPC has Constraints, which will help to keep the NPCs on what I consider an even keel.
Constraints will always constrain some aspect of the NPC herself -- her race, size, racial ECL, the levels of her life presented as stat-blocks, etc.
Ingredients could be part of her, her environment, her adversaries, her allies -- anything about her life story.
Make sense?
-- Nifft