Hi,
I would like to share my answers to your questions.
Answer for the first question i.e "What are the key components of an exceptional biography? " is -
I believe that if someone is writting a biography of someone, the first thing he should understand is about the person he is writting.
a. His basic facts (age,name,gender,birthplace,work etc.)
b. His emotional facts
(habbits, nature, relationships, understanding)
c. His vision & mission facts
(What has he done, why to write about him, what to be conveyed through biography to the audience or we can say tracing the mind of the person)
Answer to your second question I guess is the personality himself is the source of your necessary details unless it is an fictional biography.
For fictional biography the major person would be the writer himself and his vision, what he actually wants to convey to his public?