ISBN, LCCN, etc.
I got my ISBN for the book's paperback version. I applied for an LCCN. Then I worked on getting the images integrated into the book. I don't want lots of blank space before an image appears. Sometimes I had to smoosh the image a bit so it would appear in that blank space. Caption for it would also have to appear with it, and many had to be resized so they don't go beyond the new smaller margins of the image. Another tactic was to move paragraphs up to fill the blank space. Kind of tedious, but nice to see things come together. The big unknown is whether much of this translates when uploading to Amazon KDP. (Yikes, another acronym!) At least I know what I want each page to look like, and some techniques to get it there.