So you have the beginnings of a plan — now let's figure out how you're going to talk about it! Your communications plan doesn't need to be detailed, but it's helpful to start by identifying key audiences you will want to communicate with regularly. At your most basic, you should include the instructors, Ambassadors, students, and Wikipedia community you'll be working with. But think more broadly, too, about fellow education program leaders globally, journalists, colleagues of the instructors you're working with, etc.
Determining a communications strategy doesn't need to take a lot of time. But consider each target audience individually. How are instructors best reached? Wikipedians? Ambassadors? Pick a medium that works well for each target audience. It can be something like an email listserv, a Facebook group or page, or a central organizing place on-wiki. Whatever works best for your target audience is what you should consider. And think about how frequently updates to each of these groups should happen. You'll want to be able to share successes, challenges, and changes to the program as the term goes on.