Set the font and formatting in Project / Project settings / Formatting
Check this option:
Then save the project as a template.
→ If you want pre-existing documents to adapt to that new formatting, convert them to default formatting before saving as a template. Else, if you have no documents (yet), you’re good.
To avoid scattering your disk with thousands of empty RTF files that contain nothing more useful than “use TNR on nothing”, files left empty are automatically flushed from the project and not saved into templates either.
As @Vincent_Vincent posts above, this is the right way to create a template with a different font setting than the global default. What you were trying would only have theoretically changed one item anyway. The moment you inserted a new binder entry it would have gone back to the actual default.
Now if you do want document templates that set a particular font (useful for off-the-record notes in the Draft, for example), then just put a little starter text in the editor, apply your style to it, then leave it selected. This (a) creates an RTF files that gets saved and (B) when used, the text remains selected meaning you can just start typing right over it to delete the starter text.