Choosing to use Facebook as the main form of communication with your members, aside from email, is not a bad choice. It is free and most people have a Facebook account nowadays so connecting is easy. However, there is a significant risk taken in giving someone else control and management over your data. It's important, now more than ever, to evaluate if your organization needs the extra protection that a private platform, such as an online community, offers or if social media provides a comfortable amount of safety for you and your members.
If a private platform sounds like a good fit for your organization, getting this project started now rather than later will give you significantly more data in the long run and more "land" to build on, so to speak.