Is it a best practice to have a template with one master page?

> Should I copy one set of Master Pages to all files in the book.

That can be risky. For example, in our work, the Index book component has a different layout (3 column) for the default Left & Right pages. Also, the cover file has a different MP for Blank pages (completely blank) vs. the BODY file, where Blank pages still have visible header/footer content.

And, of course, as layout styles evolve, it's handy to not have lots of old documents carrying forward old page layouts. So we trim files to just the MPs they might actually use.

There are two schools of thought on this. The specific sub-template approach or the "kitchen sink" approach.

In the "kitchen sink" (i.e. everything, including the...) approach, the FM template is loaded with everything required for the project in a single file. It's simple to deploy, import it to all files and you're good to go. However, the author may have to deal with all sorts of superfluous tags and page layouts in some specific file types, like the cover pages, TOC, Index and other generated files. The onus is on the author to select the correct items to use from the multitude of choices.

The sub-template approach is modular approach where one creates the various components in separate template files, e.g. paragraph and character tags, tables, page layouts, etc. and combines to create specific templates for the various book components. These component-combined templates only have the minimum that is required for each type of document component. This is a lego-like approach and it provides more flexibility (IMHO) with modifying, updating and creating new templates. This is easier (perhaps less intimidating would be a better term) for the author to use as their choices are much more limited in any given context. However, they do have to apply the correct templates to the specific book components.

In all cases, you need to document the usage of all components in the template(s), so authors will know the intent of each and every tag, table, sttyle, page layout, etc.