If you can trust the MD to really handle the music portion and you feel comfortable choreographing or have a good choreographer I really think that the important thing is to do a show you are very familiar with. You're probably aware that a lot of film versions are not the same as the stage shows so it needs to be a show you've seen produced on stage. I'm not saying you need to rip off a production you saw just that having seen a show live may help you see that when brought to life it's not nearly as intense or may give you ideas of what you can and can't do.
Things to think about would be the talent available , do you have a few or a lot of strong singers, dancers and actors? What are their vocal ranges. Costumes for a musical can be more involved since you may have a much bigger turn out at auditions and end up with a huge cast, which may also effect your set design (to accomodate more bodies onstage) and overall budget. How big is your stage?
Are you wanting to do a show where the songs advance the plot? Are more comfortable with directing the drama portion versus the acting while singing? If so stay away from shows like Jekyll & Hyde, Seussical and Joseph and the Amazing Technicolor Dreamcoat. They are either all singing or mostly singing and require large casts.
Currently~ Miss Myrna Thorn in Ruthless! the Musical
Recently~ Emma Carew (Jekyll & Hyde), Sister Mary Leo (Nunsense), Demeter (Cats), Tzeitel (Fiddler on the Roof)