This may be done only in the presence of an advisor. You must make your decision before the recommender writes the recommendation. Each form has a place for you to indicate whether you waive your right of access or not, and you must complete that section before giving the forms to your recommenders. Use this as a guide, and write a short autobiographical sketch to give your recommender. Many professors will also request a copy of your resume.
Personal recommendations are optional.
Varies widely-see AADS application. Generally, schools will want two to three recommendations, most frequently from the sciences. The number varies from two to three. See the instructions from the medical school, but plan for contingencies. Typically, two to three academic letters.