Sounds like a cool idea.....and in the spirit of avoiding a complete clusterfuck here are a few things to keep in mind.
Someone that knows how to mix/align tracks needs to be in charge.
Then it all really begins with a drum track....and you should also put some timing clicks at the beginning of it for alignment.
Then divide up the chores however you wish.
It's important that you have everyone send their individual tracks with no drums or anything underneath to the producer (but keep the alignment clicks at the beginning.....or the final mix will be for shit....been there, done that! The order is pretty straight forward....drums, main guitars, bass, leads and vox.
Sign them up and knock it out!