Several issues with BOOKS which is a downgrade from using iTunes for audiobooks

To stop the Books app splitting the book into separate albums, the tracks can be manually joined in the Music app using for example track 1 of 30, track 2 of 30 etc. When all metadata is fixed it can be imported into Books as one.

Here's a user tip you might find useful: Organizing audiobook chapters - Apple Community

Can't help you on the album art as I always got it from Goodreads.com and added manually. But for the Book app and uploading a book to my iPhone it's very easy in the Finder. Just select Audiobooks after selecting the iPhone in int sidebar and then check off the books you want to sync.

I rip by books with Audiobook Builder from the App Store to rip and move the audiobooks to the Book library. On the iPhone I use Speedup Player Pro from the App Store.

With iTunes I had a hit or miss with getting album art so I just got used to getting the album cover art from Goodreads.com.

Just some food for thought.

The files have to be manually managed. Most of the information can be done with the album selected. For example in this screenshot, the author, name of the book and genre, and the amount of tracks is listed with the album selected and control click > get info (the album artwork can also be added at this stage, although for some reason it's not showing, but it is there):

Then using Get Info for each track add the track numbers ie track 1 of 30, track 2 of 30 etc etc etc, as shown in the 2 screenshots below:

The folder can be dragged out of the Music app onto your desktop and imported into the Books app as one album.

Lee Rodgers wrote:

Thank you. Is Audiobook Builder better than using Music to rip the CD's?

Yes. Because you can select the size of the files imported into the Book app. I've migrated to just two or three files depending on the size of the book, i.e. no. of discs.

You can try it for free from here.