How big is the congregation? I'm assuming a large one if you're able to do a musical using the members of the church. As a precaution, this will take way more time than you're planning on - especially if you're doing all three. If it's a large enough congregation to be able to afford it, I would strongly recommend asking for some form of stipend from the church, even if it's just $200. It will make them appreciate what you're doing a bit more. Some churches even pay their sound techs, and people like being techs at those churches because they're treated properly. At my church, I never got a penny for the countless hours of work I put in around services, and people seemed to think I was essentially slave labor. They'll treat you better and make sure you get what you need if you're getting paid a little bit.
That having been said... at your first meeting with your production team (you, ASM(s?), assistant production managers, etc.) explain to them that even though this is a very informal setting, you do have expectations (at which point you'd lay out your expectations for timeliness, as well as what you expect from each person individually in terms of commitment to the production) and for the sake of your sanity, the sanity of all those involved, and the project itself, that the expectations must be met. Doing all three is a HUGE chunk to bite off, and you're going to need to learn to rely on your assistants and not try to do it all yourself (which is my tendency).
What type of musical will this be? Will you have a full blown orchestra/band, or just be using CD recordings? Is it going to be entirely original (including music) or is it going to be a conglomeration?
