Hey don't worry Helen, I'm quite new to this whole personality stuff too. I just wrote down my own observations on the issue.
I must confess to not reading much of Chesterton's fiction. And Everlasting Man is on my to-read list, but havent been able to obtain a copy yet. I have read through Orthodoxy and Heretics. I'm hoping to read Dale Ahlquist's latest book talking about seeing the world from a Chestertonian perspective. Not to mention Outline of Sanity.
Concerning Buber, I'm somewhere between beginner and intermediate. I have a copy of I and Thou, Eclipse of God, and the Knowledge of Man. I also have the anthology The Writings of Martin Buber edited by Will Herberg. I would recommend this, since it provides a good overview of his philosophy along with access to some of his lesser known writings.
You could also try Martin Buber: The Life of Dialogue by Maurice S. Friedman, who also wrote a three-volume biography of his life.
I'm hoping to get my hands on a copy of Paths in Utopia, in which Buber meditates upon social and political issues. Along with Two Types of Faith.
Of course with all the other authors and writings I'm trying to get around to reading and meditating upon. Geesh, it's enough to give one a headache!