I'm going to be manually binding the pages I print to turn it into a physical hard-cover book.
To do this, I plan to print it on letter paper, fold each paper in half, and hold it horizontally to make two leaves (four pages) per paper.
Since letter paper is 8.5" x 11", I figure this means my pages must be 5.5" x 8.5" to account for folding in half and rotating it horizontally.
This also requires imposition to get the page ordering right, while still being able to print two pages per (one side of a) sheet.
And due to the binding I'm using, I don't need the margin-adjustment that double-sided usually comes with.