Yes, 'add to the beginning of the book' can be taken both ways the start of the main book html, or the start of the book's opf. The fact that the internal toc works in Previewer but not on the device makes me think it's a bug. I think total newbies like me make the mistake of looking at single html templates online which claim to be a solid base to work from.
It would really help if Amazon included a simple bare bones best practice set of files for people to populate themselves without trying to cobble solutions together from all over the internet. A lot of which add problems rather than solving them.
Seems to me like a lot of pain could have been avoided if they could be bothered to write better docs, and include a few simple example files.