I think that Patrick has pointed out a central difficulty in your
planning--if the writers arrive with what they consider a finished
product then you will not get an integrated product--if that is waht you
are aiming for.
I suggest that you consult some of the texts on project management that
exist in professional communication texts.
These texts attempt to articulate the kinds of group practices that exist
in organizations--and they will also point to some of the problems you
might encounter in terms of group dynamics.
The texts will, however, provide you with several different models. Some
models suggest for example that you divide the various writing tasks,
that you build recursion into the process (time for editing) etc. They
will be useful espcially for your real audience--the instructor you are