You have answered the volume question. Volume is the number of people who must be in your universe in order to accomplish what you want. Don't confuse universe with pipeline. You draw from your universe to fill you pipeline. Marketing is the knowledge that helps you identify who you should approach and how they should be approached.
Most people think of marketing as the active process of getting in touch with people.
That's only half. The first half is doing the research on who to approach and how to approach them. The second half is making passive contact with them. Prospecting is the active process of making verbal contact with the people in your universe to help them into the pipeline if they're qualified. Prospecting fills your pipeline.