How can I get the ‘inserted image in the post’ to also pop up into a lightbox view, as the featured one does?
This you can do by following this video:
And maybe this will help with pulling the featured image automatically for facebook:
Note: The article says it’s for the Thesis framework, but I went thought everything in the article, and it doesn’t seem anything there is actually specific to Thesis. It all appears to be just something you could do with WP in general.