Your project sponsor is Shirley, the Chief Information Officer. She is a member of the hospital leadership team who controls the IT budget and resources. She understands the requirements and how the portal will integrate with other systems. Shirley wants you to use agile project management practices to deliver the functionality in increments, ensuring a high-quality solution that meets user needs. You review the requirements and technical approach drafted by the IT team and they seem complete. Shirley is anxious to begin and suggests that you start release planning. What is your first step?