You are a much braver man than I. History is always a subject that is fascinating and perilous: Biography is doubly so. In biography you are righting the history of a person; it is hard to avoid the twin errors of hagiography and screed. It becomes even more difficult to avoid partisanship and error when one is writing about religious figures and religious leaders.

When a biography is done right it is a revelation. I just finished an audiobook biography of Francis Bernardone also known as Francis of Assisi written by G.K. Chesterton and it left me hungry to know more about the founder of the Friars Minor. The book strikes a perfect balance between story and history; between faith and reason. It explains the man and the age; and it explains both with wit and sympathy. Saint Francis as he is known to Christendom was and is a dynamic figure to the World. He gladly became God’s Holy fool. He was an ascetic and a mystic, perhaps a man that Sufis might be sympathetic to. It was claimed that he managed to impress the reigning Calif of the day.

Be that as it may, Francis Bernardone is a man that is very hard to write a fair biography of; G.K. Chesterton does, Thomas Cahill gives a very interesting thumbnail sketch of Francis of Assisi in “Mysteries of the Middle Ages” but far too many “biographies” fall into hagiography when Francis is concerned. The worst offenders are (surprise, surprise) written by either members of the Friars Minor or other Roman Catholics.

Again, good luck on the project. Choose your sources well, and keep a discerning eye out over-enthusiasm. Good biography always starts with recognizing the humanity of your subject. Even the last prophet had bad days at the “office.” (from what I have read he had one really bad year!)
It is best to remember these things when we write about people, even holy and enlightened people.