'Any ideas on how I can establish the relationship with the teacher the first few "scenes"? (without saying it out loud, of course)' ~ fairly easy, i think: start off with a training excercise. a bit more complex would be to have her in the midst of a competition and her turn is called up. this satisfies those who want to start off with some kind of action, and it's the perfect opportunity to put in subtext, which is great for eliminating a lot of overt telling, and you can use a bit of dialogue, too. the tone of the dialogue is very important to establishing their relationship and characterization.
'Would it be more powerful to kill the teacher before or after the first "mission"? (Would it be the moment she started doubting her faith, and then the incident on the mission would solidify the doubt, or vice versa?) Though either scenario will be spectacular, I'm sort of leaning towards killing him after, because I think that will be the more "epic" moment, but it's not as naratively interesting. However, doing it before will make more sense, but it's not as "visually" pleasing.. I got a decitionmaking disorder, I know, but I can't help it!' ~ it doesn't matter either way, imo, as both have dramatic elements worth exploiting. since you mentioned 'first mission,' then offhand i'd say after the mission is over. then again, generally speaking you find the mentor in the hero's journey killed right before the main climactic scene unless i'm mistaken. that's why i say that since there appears to be many missions, it probably doesn't matter.
'I would say, use a flashback of a formative moment in the MC's life, early in the novel, to show the student's relationship with the teacher. If the scene has conflict, so much the better.' ~ here, and this is all subjective of course, i'd save this flashback for immediately after the mentor dies and have it be germaine to her emotions. for example, some wise bullshit about death he told her on the porch as rain pooled around the body of the mongrel (dead in the mud) she'd been feeding. an attempt to connect that with the ending is a good thing. using a flashback 'early on' merely to establish a relationship and/or characterization from ten years ago is moot for all intents and purposes, imo, unless there is a reason why we need *more* relationship/characterization. you can completely eliminate the entire point of a flashback in your opening scene with a single line of dialogue that goes, 'why, master, thank you. hard to believe you're the same man who used to beat me for dropping a grain of rice.' so that makes the use of an 'early on' flashback good for nothing but author excess. if you haven't established their relationship by the time of a flashback, you haven't done your job ~ that relationship should be obvious from the very first scene. i'd avoid a flashback unless you're also telegraphing what's to come in the climax (in this case). just my opinion.
'I think constricting a story to a specific medium is a limitation, not a strength.' ~ you will likely fail then. i had the same question willow had about it being a novel or a script. a reader doesn't want to read a prosey script any more than a producer wants to read a lopsided adaptation what doesn't fit generally into the step process if it's to be a mainstream project. it really sounds to me, and excuse my bluntness, that you're being a selfish writer by seeing the movie version and just writing that down with no consideration as to how the reader will accept it as evidenced in this continual flashback idea. then, when the reader asks what the hell you're doing, it's their fault for not 'getting it.' is there a reason for all these flashbacks? i mean is there really a need for them that you can't accomplish without the quasi-experimental aspect? i'm sure it'd be fun to watch, but it sounds rather annoying to read: i'm afraid it sounds like a monumental waste of my reading time to slog through just because you don't want to adhere to any one 'medium' and learn to write effectively. montages work in 'rocky' movies, but if your name isn't jerry bruckheimer, you definitely should get *a lot* of feedback before relying too heavily on this scattershot opening scene that 1) removes all mystery and 2) sounds as if effective writing is totally being ignored, i.e. all style, little substance. ('but, preyer, 'kung fu' used flashbacks all the time!' great. when this story is made into an hourlong drama for commercial television, i'll cede the point.)
'Like I said. I'm creating a story. A good story won't be bound to a specific medium. Granted, the story is told in slightly different ways for a novel and a movie (and computer game, tv series, stage play or cartoon) but the fundamental story remains the same.' ~ actually, an effective story will be bound by the medium's conventions, yes indeedy. movies and novels are told 'slightly different'? imo, if you believe there's only a slight difference, you're either naive or deluding yourself. there's a very good reason why producers don't have the novel author write the screenplay as a rule. it's why a few agents almost specialize in writers who are good at book-to-screenplay adaptations.
'What I do is I create a story-foundation which can easily be written into different formats right from the start.' ~ who doesn't? sorry, but i think this statement perfectly illustrates egotism borne from ignorance and pure, unadulterated newbie-ism. playwriting, screenwriting, journalism, novel writing, etc., are are individual crafts in their own right. even novelists aren't necessarily good short story writers and vice versa. every single idea we all have can be adapted to any other medium (though it's best done by someone practiced in that medium usually). whether or not that adaptation is successful, well....
basically, conventional wisdom is don't confuse a script with a novel. too, don't think that it's easy as all that just to knock out a script version of your novel. for that matter, folk shouldn't think that screenwriting is a lower form of the written word and it's based on a forumla anyway, so anyone can do it.
'(Granted, it's a lot more work, but it ensures that the story is water-proof, because I have to see it from many different angles while in the creative process.)' ~ it sounds more muddy than water-proof to me. how is your approach ensuring anything, let alone making sure your reader's experience is the best it can be? i honestly believe there are writers out there who writes the movie in their head into a novel form believing some producer will see it and say, 'hey, let's buy the rights to this book! the script is practically already written out for us, right down to the camera angles!' then the writer wonders why their story, which isn't a bad idea, doesn't work as neither a novel nor a screenplay.
there's certainly a great amount of information you can take from screenwriting and apply to novels, but you have to know where to draw the line, too. you never hear of a novelist talking about beats, and rarely about Act I, II and III. by the same token, you're not likely to get far as a screenwriter without knowing what purpose Act I, II and II serve. same story told differently, and hardly in 'slightly different' ways. what's important to a novelist to see on screen doesn't necessarily mean squat to a screenwriter.
back to the point and to reiterate, i don't see the benefit of multiple flashbacks just to show characterization/relationship other than showing off some gimmicky montage sequences a director may someday get a chuckle out of then proceed directly to doing the movie exactly the way he wants. i guess what i'm saying is once you start directing a novel as were it a movie, that's obvious to the reader, is rather annoying to read imo, and doesn't move the story further when conciseness is one of the keys. flashbacks and prologues divide the writing community right down the middle, but i think most of the reasonable anti-flashback/prologuers will admit that if it's appropriate and moves the story along, okay, go for it, but make sure you're not abusing them.
killing the mentor is standard hero's journey fare. having him actually live is being different. if you wanted to be different, just have him leave for his own quest.
as an aside, i'd argue that the premise is flawed in that training doesn't encompass the real world, unless the 'chosen one' is never meant to leave the temple or whatever, and that in order to accomplish a mission she'll have to have some social skillz, knowledge of culture other than her own and on a practical level, and basically knowing how not to get run over by an ox cart because she's standing in the middle of the street staring at a flagpole. here's basically what i get out of it: 'you can kill anyone in the world with ease. now that we've completely isolated you from as much diverse human contact as we could, please go out into the real world and do a job for us regardless of how unprepared you are because we're too short-sighted to consider this possibility in the 22 years you've been here training to kill, because, you know, if you can kill people you can go anywhere and do anything.' it's hard to imagine her having a healthy, normal relationship with anyone let alone her mentor. i know, by keeping her isolated, the loss of her mentor is greater... i guess. i don't know, though, it strains my suspension of disbelief to think all she's done for 22 years is train to beat the snot out of people. i mean, does it really take that long? couldn't they have slipped in some field trips? lessons on table manners? how to act like a lady when she's not assassinating people? at least teach her to dance? i like the idea of her destroying her own faith as an act of rebellion then trying to find it again once she feels the regret for her deeds. anyway....
you raise someone up like that and you'd probably have a very angry, resentful person who just happens to barely keep herself composed due to discipline (and not wanting to be beaten). hell, she should KILL her mentor, the bastard! then feel sorry for it later, but, yeah, this guy's ruined her life basically by feeding her a bunch of cultist horse hockey and not giving her any life options... which would be one (shady) motivation for her isolation, but also the fastest and easiest way for her to want to get away once she finds out how life can be, i think. at any rate, the point to consider the motivations. the nice thing about a novel is you can elaborate almost as much as you want as opposed to a script where time's ticking away. still, even with the extra freedom in a novel you can't drone on endlessly.
sorry if i seemed mean, proto, not my intention, but being a guy who gets a reality check pretty often keeps one humble. that's why i say stick with writing a novel or a script ~ you can't really kill two birds with one stone and make either as effective as they need to be.