I think you get it quite right with one exception: The autopost feature sends some text (in "message" parameter of facebook API) to facebook. Usually text contains link to the post (via {%AbsoluteUrl%} macro).
But facebook will only convert this URL to hyperlink in body of a post and will not process it.
You have to send URL in "link" parameter of facebook API in order to make facebook process it. And this parameter isn't accessible in Kentico, since underlying SDK doesn't support it.