I thought your "public domain" comment was probably parabolic, but now I'm certain... ;)
Depending on the book, the topic, and the magic pixie dust called "virality," Amazon books seem to range anywhere from total flops to raging, life-changing successes... A couple of cases in point would be "The Martian" by Andy Weir, and "Wool" by Hugh Howey.
So, when will you begin writing your book? That's the problem with interacting here on Steemit; you loose pretexts and excuses when you start to expose your thoughts and intentions... You know, peer pressure starts to kick in? ;) :P