Nice work on finally bringing HTTPS support in!
I want to note something on point 4 (emphasis mine):
Rebake remaining posts with HTTP images, so that images linking to HTTP addresses will become links - most of those are dead anyway.
If most of those links are dead anyway, why not go through the hassle once and check if they are actually dead or not. If they are, just omitremove them! Why would we need to rely on the community to fix one by one if we can do this automated at once?
It seems automating this is difficult, so m0sa set up a crowd sourcing project to let us do the work do manually. Please contribute if you can! About 2500 posts to go...