A common barrier to getting started is not knowing how big or small to make something. Should this book cover this subject and that subject? Where does one end, and another begin?
Try thinking about cell division, when the cell of an organism replicates as the organism grows. Go ahead and let your creation be a borderless mass. It will become clear when it’s time to divide it.
If you think about cell division, you’ll have one less thing stopping you from getting started.