There are no templates for font-sizes in GeneratePress, and I’m not aware of a plugin that offers such a functionality.
Alternatively, you may try creating a mock/staging site, and import a site that has an ideal font setup for you from the Site Library, and then take note of the Font settings in Appearance > Customize > Typography, and then replicate the Typography on your actual site. You may also try exporting and then importing the Typography Setting only through Appearance > GeneratePress.
Hope this clarifies. 🙂