The sequence for deciding whom to include in your work is:
Think about how to involve more than the usual people based on the six categories: people who care, people with authority and responsibility, people with information and expertise, people who will be personally affected, people with diverse points of view, and people who are considered troublemakers.
When considering how many people to include, think whom you must have to succeed and who would be nice to have to support the work.
When thinking about whom to involve at what stage, chunk out what you see as the stages and think through the characteristics of people you would like to include. Remember you'll have to adjust as you go along due to unplanned circumstances.