Selling old books using self-publish?

I’ve acquired a few very old books with the intention of reselling, but started exploring the possibility
of digitizing them so that I can make them available for selling on demand and keeping the (very cool) original copies for myself. What I’m interested in doing isn’t really covered in the general book-selling guidelines that I am finding on Amazon. Can you all help me with any of the following questions:

What is the best way to scan in an old book to make it suitable for new binding? Am I correct in understanding that these copies are printed on demand, when a customer orders? (Seems improbable to me but something I’ve read elsewhere makes me ask.) Or do I have to pay to print a particular quantity to begin with?

And of course I’ll be sure to verify that they are definitely in public domain – one is for sure.

Thanks!