Why the plural form? IMHO a single template file is enough and probably mandatory to guarantee homogeneity and ease of maintenance.
This template contains all styles and a sketch of the volume as cover, introduction and dummy chapter. You’ll probably find advantage to also create an AutoText entry for the dully chapter so that adding another one is a treat.
This the role of the template file. Styles are stored there. Your volumes are based on the template.
But this is defeated if you don’t follow a very strict discipline regarding styling. Prohibit any direct formatting and style definition in your volumes. Use only styles from the template. Modify styles in the template only (document styles will automatically update next time you open a volume).
At writing time, don’t bother with style appearance. At start, give your styles small differences, just sufficient for a visual feedback telling you you applied a style (paragraph or character). As a consequence don’t name your styles for their visual effect but for their semantics (Body Text, Heading n, Definition, Comment, Emphasis, Strong Emphasis, Quotation, Footnote, Endnote, Trade Mark, Foreign Word, …). This gives you full liberty to format them the way ou like while keeping the mark up permanently relevant.
You can do with a single page style, the header of which is “computed” with fields. Fields retrieve information from the “discourse area” to insert it into header. There are fields related to chapter utline which get their value from Heading n paragraph styles. Use them to style subject headings and subheadings.
A book like an encyclopaedia will make heavy use of fields (and cross-references) so that the complete document remains consistent. You can even achieve a higher level of automation by defining custom entries in File
>Properties
. These entries are also retrieved with fields, just like all other properties. Think of the title itself. Define it in the template and it is available for all your volumes without the risk of a manual typo. Change it in the template and it is changed in all volumes!