I'm just going to go for it lol.
And pick up the pieces as i go along.

Thats a great checking list you posted above.

I'm still looking in to this addition and that is to force https via a .htaccess file

Code
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

I done a test on a basic site of mine with out forums, using the following via my server.
Use a symbolic link from private_html to public_html - allows for same data in http and https

Which then deletes the private_html leaving only the publc_html

However i was not getting the secure icon etc... until i added the htacces lines above and that seems to be working as expected.

Hopefully migrate over later this week using my forums.
I'm not on version 7.6 at this time.

I want to get https settled in on a working forum and then upgrade.

My thinking anyways.

BOOM !! Version v7.6.1.1
People who inspire me Isaac ME Gizmo