Figure out to whom you are speaking
In making an argument from sources, you are aiming to persuade a specific audience--you need to identify your audience early or risk making an argument that is ineffective or that no one cares about.
Choosing an audience is relatively straightforward.
For researchers, choose a venue for your argument such as a specific journal or conference.
For practitioners, your audience might be a specific client such as a school or organization, or a broader audience such as "high-school biology teachers" reading a online publication you write for, or an op-ed you plan to shop around. Because you are writing a written argument, think about what specific audience you are trying to reach and how this argument will actually reach them. Even you started this for a class, treat it as an article you might publish in the future.
Once you have identified your audience/venue, add it to your master design document.