HTML template not used for header and footer

[Foitn]

In my previous issue #9463 I requested the use of header and footer to be added through a template.
This has now been added, but not in a way that is very usable.
I have several issues with the current implementation.

Template is not using html files

When I try to use the pdfHeaderTemplate, I cannot use it like the cover page.
I have tried the following:

pdf: true
pdfTocPage: true
pdfFileName: TestDoc.pdf
pdfCoverPage: articles/TestDoc/0-cover.html
pdfHeaderTemplate: articles/TestDoc/0-header.html
pdfFooterTemplate: articles/TestDoc/0-footer.html
items:
- name: Introduction
  href: 1-introduction.md
- name: Some amazing content
  href: 2-some-amazing-content.md
- name: Conclusion
  href: 3-conclusion.md

When I generate this, the cover page is properly added, but the header becomes (very tiny in the top left corner):

The same goes for the footer

In the toc.yml file, if I add the full html of the example/default I get an error, since the html contains a colon (:) since html works that way.

The header/footer are not added to the TOC page

Nothing is added on the TOC page.

What I would like

In the end it would be great if I can add a template for both header and footer in html file (or md which generates html files).
I have added the following zip, that contains all files that could be turned into a pdf file.
This PDF would contain 3 chapters, a TOC and the front page.
Each of these files would receive the header and footer as provided.

TestDoc.zip