So far we've done mass market fiction paperbacks whose authors start with the letter A. So no non-fiction, no oversize paperbacks, no trade paperbacks, no hardbacks, and nothing from the other 25 letters of the alphabet. (And no Trek/Star Wars, either.)
170 of them, 3.5 metres, and that's after removing 8 duplicates.
I can see this may take some time - going on this basis, we may have about 4,000 in total.