Suggestion: Provide a setting for the default font size
The summernote documentation shows it is possible to set the fontsize with eg $('#summernote').summernote('fontSize', 20)
Maybe a setting could be provided to configure a default font size? That is used alongside the font units so maybe have a second setting for the units.
See https://chat.civicrm.org/civicrm/pl/7hyjhiobkbrkfbb5y6j6huitzr