Can't finish my ER diagram
I would say that an Edition is an entity that is related to a Book.  

You then have a one-to-many relationship between Books and Editions.  (One book can have many editions.)  and a many-to-one relationship between Editions and Publishers  (many editions are published by one publisher).  

When I was building actual databases, back in the day, I always had access to one or more "subject matter experts",  people who had become familiar with the data through constant use.  Most subject matter experts were neither computer experts nor database experts.  Your situation is somewhat different.  

I would try to find some kind of on line subject matter expert, like the Library of Congress.  They might have some kind of model of the publishing industry that would provide answers to this and other questions you have regarding how the field of publishing really works.  And this model might be in the public domain.

PS:  Congratulations on using the ER model as an analysis tool,  and not diving into database design prematurely.