From experience, leave all word building behind, because it's your strenght, and you can just take a note when you get an idea.
Break down your projects into mechanics, how does the camera behave, how does the character behave, what are the movements you will require, what are the elements in the world that can be interacted with and how will they behave...
Once you get all these, you can prioritize them, and get started on C2. You will then realise that things you thought simple are not and that they can conflict each other.
You can always justify later why this wonderfully advanced civilization decided to banish all forms of elevators and adopt staircases in all their ships.