I highly recommend checking out the Burning Rogues appendix, which starts on page 562. You'll want to pay special attention to the Deeper NPCs and Crucial Opposition sections. That's how we build NPCs in games.
I would urge you to give your really important NPCs a full burn. You can add stuff to them after. I recommend it. But burning these characters will give them far more depth and make them far more interesting than otherwise. This thread, based on one of Luke's games, is a case in point.
I corner him and stab him in the face!