1. Those are the covers themselves:
https://standardebooks.org/ If I had any idea how many people would ask this, I would have used different books. I even added a disclaimer to the github directly under the main image.
2. In the last few days I added some code to adjust that size smaller if the text is too long, but it only goes so far. Once the font gets real small, it looks bad, and I prioritize things looking nice over maximum utility. Someone could write a user patch to make the font as small as they wanted, though. I have a template and KOReader has documentation for user patches, but it would require a level of knowledge of Lua and the KOReader code base.