> ... want the footer on each resulting page in all the chapters and the index to include the Total Page Count of the book.

There is no variable for the total page count of a Book. The apparent "Page Count" variable <$lastpagenum> only delivers the page count of the current book component file, and is thus generally useless for anything but monolithic files.

In unstructured FM, the usual work-around is:

• Put a Cross-Reference marker in some Body flow on the last page of the book, perhaps in an empty paragraph or in some meta paragraph using invisible or non-printing text color.
• On the Master Pages of all book component files, in the background header or footer frame, construct the page number string, typically:
  Page X of Y
  where X is the variable "Current Page #" <$curpagenum> and
  Y is a Cross-Reference to that End-of-Book Marker, format <$pagenum>

As pages are added and deleted, run an Update Book to revise all the footers.

Now, as to how easy this is to implement in Structured Frame, that I couldn't say.

You might get more help in the Structured FM forum – this one’s for unstructured FM