Here are a few things you should consider before diving in further. They’re not here to deter or intimidate, but provide food for thought.
Does it have to be a mod?
Making a mod for your idea may sound exciting, but it may not be the correct choice. For instance, if your entire project would essentially be one long cutscene, maybe it should be a comic or a video instead. Remember that games are an interactive medium, and that OneShot specifically revolves around the idea of the player being part of the story.
Why not a fan game?
You could mod OneShot, or you could make a completely stand alone fan game instead. Each has their pros and cons, but the gist of it is that it’s a trade between freedom and simplicity.
Modding: + Easier and faster to get started + Reuse vanilla scenes and assets + Familiar to players - Depends on owning and the ability to run OneShot 2016 - Limited* to what the game already does - Style limitation - Niche technology - Learned skills may be harder to apply in other places
Fan Game: + Freedom to do whatever you want - Requires your own assets - More upfront effort - Higher skill requirement for the most part
*- The limit is how experienced and determined of a programmer you are, given that you can modify the engine and scripts.
What’s the scope of the project?
What kind of changes do you intend to make? Is it just an asset swap, or something that implements crazy meta elements?
See Layers.
Solo project, or collaboration?
And what kind of work will collaborators be doing?