Add from ISBN allows all those to bear a Tag of your choice:
<In Paper Library> is what I set.
No other special treatment needed. A simple
Empty Book
The Tag
also allows for there to be other formats (A lot of mine we Baen Book and the had many of these on the CD's or Free Library).
Back to the Limit Question: Yes, a
Single one might reach a limit (Single includes VL's), But How many disks can you attach to your PC? AFAIK, the only 'Library' rule is it must fully be on a single drive (nothing stops you from having more than 1 on your 12T drive