I approached the process in a similar "Hmmm!" method (i.e. initiating sketches, choosing favorites, and proceeding with 2nd drafts). The overall project is simple in its solution: the face of the story and its intention.
I was playing with Adobe Dimension to divvy up the book mockup (far-left, above).
The final bits are great. I love the colors. Green and red have always been a challenge (which one is darker?) for me, since I seem to gravitate towards cooler colors. I think playing with the typography and toying with the value on the greyscale helped tremendously, in this respect.
I want to make it clear, also the publisher's logo, ISBN, tagline, two-or-less various typefaces are imperative to include.