I assume you mean where to go for print on demand?
Affinity Templates for Blurb et al?
Paper choice
Book binding and covers?

The problem with so much these days is it never get printed. Though I am guilty of this as the Magazine I produce is on-line PDF only (but A4 so anyone can print it at home.  However we are also looking at doing some limited run hard cover books.

As a retired librarian I have great love and respect for print media, though many of my former colleagues have been dumping books out of libraries much to my dismay.

My young granddaughter taught herself how to publish her own books via Amazon. I was amazed at this video describing how print on demand works. Her books are delivered anywhere in America in a day or two. I marvel at the people who figured this out and got it all organized. We found that the books are not necessarily printed at the facility nearest to the recipient but at the facility that can produce and deliver it the fastest to that recipient.

Amazon Books on Demand Virtual Tour
https://www.youtube.com/watch?v=9KjPcw64Izg

I have noticed that because "it is all on-line"  and they want to have new books so the old ones go. The other thing is they want to be "multimedia" and other buzzwords. Also "storage" space costs money. Where I am the Library has been re-organised from three floors to two with the County Council using the top floor as offices.  This is bad as the 1st floor is basically a mezzanine floor, not a full one.   So we have lost over 1/3 of the library floor space.

As for Amazon.... pros and (lots of) cons.  We could do with a list of print on demand outfits and people's experiences of them?  Perhaps a thread on each one?

What I am doing for https://www.tamworthheritage.org.uk/ is PDF on-line but we are also looking at hard copy for some things. But these will be limited edition books, mostly pre-ordered, and we are talking to book binders to have a special custom book.

We have our own ISBNS which helps. If you have an Amazon one you can only sel on Amazon AFAIK.

An actual ISBN you get from here https://nielsenisbnstore.com/Home/Isbn  Some years ago my company bought a bulk set before there was a price rise. They have gone up a lot since then. Once issued they don't age., they last forever.

If you use Amazon and their ISBN they become the publisher so you can only sell via Amazon.

Mine belong to me (JAMedia)  we can put them anywhere.

Rather than dump surplus books, a better alternative is to have a book sale, selling the books at very low prices. I have seen it happen. I bought some myself.