Your committee can be as small as one person (if you have unlimited free time) or you can have several people. It all comes down to the various tasks that you need to consider. The more people you have, the more the tasks will get spread out. You are looking to create a diversified group who weren’t all together in high school. This will help spread a wider net when trying to locate people, and when encouraging people to attend.
Although some committees attempt to plan everything as one unit, it can be far more effective to break into smaller groups. When dividing the workload, try to match up the right people for the right task. Someone who works in advertising or public relations, for example is well suited to get the word out. Businesspeople may do well to negotiate with vendors.