Do the actors actually have to burst into song?
They have to sing. But it can be on a stage. It doesn't have to be random songs in the middle of conversations or whatever.
Is a movie a Musical when it has a lot of music in it but it's all diegetic?
I would say no, especially not if the characters aren't singing.
How does an animated musical scale versus a live-action musical (yes, that really matters to me because of the dance and choreography and costumes and sets, etc.)? Can I really compare The Little Mermaid to Cabaret?
I don't know if
you can, but I can.
The Little Mermaid >
Cabaret. See?
Do Muppet Movie musicals count and if so, at how many cents on the dollar versus one with live singers/dancers/etc?
They had damn well better because I'm planning to vote for one, but I see no reason why singing animated characters would count but singing puppets wouldn't.
How many songs does a movie have to have to qualify? Streets Of Fire, for example, has only a few songs and they are all performed by bands in the film, but those bands are also characters in the film, so...?
Obviously this is going to be up to your discretion and Thursday has already said she's not going to weigh in on eligibility for every movie because she hasn't seen all of them. The way I'm handling it is this:
1. Do the characters sing throughout the film or is it just one or two instances of singing?
2. How important is music to the story?
For example, I'm considering
A Mighty Wind because there is singing throughout - by most of the characters - and because the music is integral to the film's story. The is no story without it and the songs in the movie were even created for it. On the other hand, I'm not considering
The Bodyguard because although one of the main characters is a pop star, much of the music is television footage of her singing rather than her actually singing in the scenes (though there are several instances of that as well). Also there's only one other named character that sings in the movie and she only sings once. As to the importance of the music, if you replaced the pop star with any other type of major celebrity the story would still work so it's not really that important.