1) calibre will have a dedicated embed font tool that will remove the need to refer to font files at all. You just specify the font family, the @font-face rules and file import will happen automatically.
2) Image sets? How often does one add image sets to a book. Once per book?
3) House standard content that comes in multiple files? Again not a common use case.
b) I have already added a link stylesheets tool.
https://github.com/kovidgoyal/calibr...ad554412292640