I think the "right number of books" one is putting the cart before the horse. The right sized house to have is the one that accommodates the number of your current library times 10% increase for each year you plan on living in the house until you have to move because your current house no longer accommodates your library.

For those who want to do the math-- if you currently have, say 4000 books and estimate that your house could hold 6000, you will need to move in less than five years.

Ace of Spades Headquarters Sunday Morning Book Thread.