Making a book. Adding photos after the initial batch WITH their metadata titles

A 'long-winded' reply:

This is the method I might use to keep my book photos in a 'Chapter' order- BEFORE commencing the book-

1) Create a new Standard Collection.  Call it (Assembly for Book)

2) Mark this Collection as the 'Target Collection'

3) Immediately set the Sort Order for this Collection to "Custom" (even though empty- no photos!)

4) Select images for Chapter-1  (from another Collection, or folder, or selected in All Photographs)

5) Press [B] to add these photos to (Assembly for Book)

6) Repeat steps 4) and 5) for Chapters 2,3,4,5, etc

This method will keep your photos in a Chapter order in the (Assembly for Book) Collection and Film-strip.

7) Use the (Assembly for Book) Collection to start the new book.

Now because you already have spent time with your book and Chapters 1 & 2, you might-

1) In the Book module (if not already done from the tab) Create a [Saved Book Collection] 

2) View the [Saved Book Collection] in Library Grid mode and Custom Sort

3) Add your Chapter 3 photos to the [Saved Book Collection]

4) Repeat Step 3) for Chapters 4,5,6,etc

When you re-open the Book from the [Saved Book Collection] all your 'added' chapter photos will be on the Film-strip in the 'Chapter' order as you added them .

For "Title" text, I suspect that you would need to then select all the Photo Cells in the Book: [Ctrl+Alt+Shift+A] or the Edit Menu, then check the [Photo Text] box-