When I print-out for editing purposes, I use 1" margins all 'round, 11 pt TNR, with 1.5 spacing. I also start chapters on a new page, down 1", so I have guaranteed note room at least once a chapter.
When I can, I double-side the hard copy like a normal book, but when pressed for time (since I don't have an auto-duplexer or already had a bad day), I'll also print the first half of the book, flip the whole thing over and then print the other half on the backs of the first half. Same achievement, less fuss if the printer grabs 2-3 pages at a time and the "count" messes up--which is what always happens to me.
Scarlet> Did you actually have a good reason for printing out single-spaced or was it just a brain-fart?