Write the book.
And if you are hesitant about your writing style or other thoughts about the mechanics of doing it, just have someone else go over it after you get done. Remember that the very best authors all have editors that work their books over, so that part is nothing to be leery of at all.
Just get it all typed up at first,,,,,,,good writers also know that the first draft is never the best draft,,,,and don't be afraid of re-writes, those are also a normal part of writing.
I am a Technical Writer, so I would be of little help to you, but, maybe you know a friend that can step up for you,,,,,,,or someone that knows a writer or anyone else that already edits biographies or fiction,,,,,,both of those types are pretty close to the type of story you will be telling.
Be sure to let us know when it is finished, though,,,,it would be great to read another's journey throughout years of modeling.
Rex