Answer:
The number of roles: How many people will be able to participate?
The number of scene changes/scene complexity: How difficult will it be for us to design the set and the costumes?
Budget: Again, how much will we have for costumes, set design, and any other needed materials?
The subject matter: Is this something that participants will enjoy or relate to? Will we have fun? Will the community coming to watch be interested?
I would probably apply similar criteria if I was selecting a play for a Broadway show, but in that situation, we'd probably have more resources for costume, sets, etc.