The tougher part is that some of your post seems a bit misleading to me.
The couple of microformats related lines you’re adding in your child theme like
add_theme_support( ‘microformats2’ ); are in fact declaring that your theme properly supports microformats v1, v2, and microdata which it doesn’t quite. Those lines don’t actually add support (as the hook might indicate), but tell other WordPress plugins that your theme is microformats compatible which may prevent them from adding particular pieces of redundant microformats related code.
While you’ve got an
h-entry in your header file, you’re closing the related
</div> just after the title so that if the body of your post includes a
p-summary or an
e-content microformat, parsers are likely to have problems. Instead you might want to do something similar in either your
content.php (or other file that adds the body of your post) or your
footer.php files where you close that
div in one of those two files instead of in your
header.php file. If you need it the article page on the wiki has a simple example of what the final result should look like.
My favorite template for how to add microformats to a WordPress theme is David Shanske’s fork of the TwentySixteen theme. Because of GitHub’s interface and the fact that he made changes in relatively small increments, you can look at the history of his changes (start with the oldest ones and move forward) and see the highlights of what he added and removed in individual files to effect the necessary changes. (He made some other drastic changes like removing Post Formats in preference to Post Kinds as well as some other non-microformats changes, so you’ll necessarily want to skip those particular changes.) I think I learned more about WordPress Themes by going through this one example a change at a time than any of the books or tutorials I’ve ever seen.
If you need some help, feel free to catch one of the WordPress folks in the IndieWeb chat. I suspect that since you’ve got the fortitude to dive into the code the way you have, that you’ll be able to puzzle it out.