Unless I missed it while skim-reading, I don’t think you described the story idea, other than to say it’s science fiction. Some specifics would probably help entice potential collaborators.
There’s nothing wrong with tackling a large project as your first project, if you’re passionate about it. But the sheer size of the project does create an additional pitfall for the author(s).
According to the website, IntroComp is returning in 2023. You might consider assembling your starting excerpt and entering it in that.
With respect to possibly breaking a large story into sections, I did that with my Leafstone fantasy saga (easy to find on Amazon if you spell my name right). It’s one ginormous story, but it’s broken into four discrete books, with what I hope is a satisfying semi-happy ending to cap off each of the first three books. So I know it can be done, but it requires some careful planning.
With respect to your original post, you mentioned wishing for some help with the narrative and pacing. Unfortunately, pacing is impossible to control in an interactive medium. It’s probably easier in a choice-based system like Twine than in a parser game system like Inform, but it’s still not something you can control.
The narrative core (nice phrase – I like it!) is the story you’re hoping to tell. You might find it useful to pick up a couple of books on how to shape a story in conventional fiction. In IF, the rising action has to be handled a bit differently, but giving your lead character a clear goal that is both important and difficult to achieve is exactly the same, in my experience. In the absence of a clear, important, and difficult goal, the narrative is just going to flop around.