I go with 1 book for every LBOD/color combination for tailor & smith, for rewards I would want to have. If something doesn't produce a decent reward, it just gets stuck in a book for potential bribing or selling. It's a lot of books (probably about 50 smith and 30 tailor), but I've had over 10 years of being given books of BODs to be ready. Hell, I had enough leftover books that I'd emptied that I was able to use those 5-10 year old spares to fill the first couple of Bulk Order Book BODs my scribe got.
With the tailor BODs, I only keep 1-4 sets of smalls in case a large shows up (and any low-end larges get bribed immediately to where they would be useful). Most smalls, these days, go immediately into unordered books for cycling (filling to get new bods) or selling, as I have multiple sets of every 6-part small BOD ready (some of them already filled). Only the occasional Studded or Bone small finds its way into my books.
Smith BODs, on the other hand are few and far between, so I rarely have a full set of any of them (despite having 6 BOD runners).
Come to think of it, I need to get around to sorting BODs and restocking my vendors - my lockdowns are full again, and with the events, hadn't done any BOD runs.