Hey there, fellow writer of fanfiction! Your idea of putting ME characters in a high school (of all places) is a very interesting idea. I myself have been writing a close-to-but-not-really-similar-story. (TOUFA-that's just abbreviated because the name's too freakin long)
If you desire for your chapters to be shorter, might I suggest that you put a little more detail as to how the school looks, it will give the readers a better idea of what you envision.
And I read that you'd like some character ideas, well I'm not sure what you already have in mind, but here's a few spitballs: Perhaps have Samwise and Rosie hold a Home Economics class, or have Boromir teach Gym. Just a few ideas.
Oh. And I would totally freak the hell out if I knew Boromir was even near me. ;)
Happy writing, I hope this helped.
Author's Response: Thank you for your feed back! I guess I probably should describe how the school looks. And your ideas for Home Economics I just might use! Thank you!