Your church has a great story and has had great success in an area that many churches struggle. I think you'd really want to get this unique story out - I know from experience that it's hard to start a deaf church, and that you guys have done it so well is really a testament to God's greatness and a lot of hard work on your part.
I like that you want to produce it to help other deaf ministries.
There's an interesting book called "Documentary Storytelling for Video and Filmmakers" by Sheila Curren Bernard that focuses, as the name implies, on the storytelling aspect of doing such a project. It's on Amazon and other online book retailers. Any of the books in the DV Expert series are really good from a technical standpoint.
I'd also recommend watching documentaries, beyond what is shown on TV. Rent some feature-length docs that tell a good story (like anything by Ken Burns - the man needs an editor really badly, but he can tell arresting stories!)
I always like to have people tell their own stories. If you could have some of the people in the congregation tell about how they came to the church, and the difference it has made in their life, you're halfway there!
Of course, you'll want the church leadership to cover their vision, why they built the room and the church the way they did, and so on, but keep in mind that the meat of your video will be the lives that were changed. That will be the most inspiring aspect of this project.
Keep us posted. I know I'd love to hear about how the project is going!