No, the words are bigger in the kindle so there won't be as many words on the page of a kindle as there are in a book.
The word for this is "similar." The same shape and the same size is "congruent."
Yes, a lot of books have more than one cover but its still the same book and everything written inside is the same
Yes, there are just collectable covers.
They can. Most of the time they do not have the same plot, but many books have other books that share their title.