Almost none at all.
Your job is to convey your information to me as efficiently as possible, at the start of the writing process. With an autobiography, this means a series of recorded interviews, usually face to face or on Skype audio. They have to take place at the start.
Then you can get on with your life.
Perhaps you’ll have given me photographs, cuttings, transcripts or other documents. I’m an experienced researcher and fact-checker with subscriptions to many archives and libraries so if necessary I can undertake background work as well. Just leave me to it.
I may be rewriting and adding to some text you’ve already begun, or working from other research. If so we will work out before we start whether interviews are necessary, or whether I need to watch films or read letters. I don’t often misjudge the time a book will take. If there’s plenty of written work and not much interview, four to six weeks can be sufficient for a short book of 30,000 words. On the other hand it takes about four and a half calendar months, including six weeks of ‘research’ (including interview) time and two weeks of ‘publishing options’ (including ‘amendment’) time, at the end to complete a publishable 70,000-80,000 word typescript – a fairly typical autobiography. (See my blog on translating ‘thousands of words’ into pages.)
That’s a relief! You don’t have to write a line. So…