Great to hear from you, lmm! Thanks for reading my article.
It sounds like you are taking great care of your photos. It's always good to make a copy and store it safely (from possible water, fire, etc. damage.) Personally, I use copies, especially if I'm doing any cutting/cropping. I would also consider who might be viewing the book - will it stay on a shelf or will children be going through it someday? If you feel confident that the copies are safe, you could use the originals.
Another idea... when you get the digital copies, make a digital album! Then, no one is touching originals and you can make multiple copies, if needed.