I'm working on planning what is supposed to be a semi-realistic multi-chapter, two part story about a group of high school kids. The story will focus on each of them individually at some point in the story. In part one, one of the main characters starts cheating on his long-distance girlfriend who is away at college. They met through his younger sister, who is close friends with the boyfriend and also another main character. The older sister/absent girlfriend (I'm going to call her AG from now on) isn't present for a lot of the story and none of it/almost none of it is written from her pov. It is acknowledged, however, that both girls have mental problems (depression, social anxiety, that kind of thing) and that AG's are not treated. It's also mentioned that AG is having a tough time at college. Either at the end of part one or beginning of part two, AG finds out her boyfriend is cheating on her and she commits suicide. In part two, one of the major issues is how the characters deal with AG's suicide. Is this too complicated or unrealistic for the story?
It could be, because I'm already confused about who we're talking about. His younger sister is close friends with what boyfriend? In any case, there is no answer based on what you've given us. It depends on the writing. Write it and see how it works. The general scenario you've described seems possible.
A story concept means nothing. What matters is how you write it: the characterization, the flow, the imagery, all of it. There's absolutely no benefit in asking what other people think of the concept! They'll either say,"Sounds great," or, "it sounds like a ripoff of..." If the idea stirs you, write it. Then ask people what they think of the final story. After they tell you what they don't like about it, revise it, usually several times, until you're happy with it or until you throw up your hands and say the hell with it. Please read What is Plot Creation and Development?
When it comes to complexity, you should ask yourself if you can handle this level of complexity. Intense amount of complexity can grip the reader since the reader will want to know how it will all be resolved. Ideally, you will want to balance complexity between your ability to handle it, and making a gripping story (not too much, and not too little in other words) The best way to find out what your limits are, is to just make shit hit the fan, and see what happens.
If this is your first writing project I'd pare down your character count. It's really difficult to handle a lot of characters straight off. I once attempted to publish a children's book and the publisher sent me back a rejection slip with one of the problems being the ammount of characters. I'm not saying you can't write a story with interwoven characters but if it's the first thing your attempting it's hard to pull off. I too, have a story with a high character count and interwoven stories - I've written two drafts but still don't feel comfortable with my ability to pull it off. I've actually put it on the back burner until I can come back to it and feel like I'm doing it justice.
