This is a an impressive system you’ve cobbled together. I’ve been thinking much along the same lines recently. As for the issue of posting to Social Networks without a corresponding blog post, is it possible to have a social post category that does not display by default on the blog? For example, some ephemeral item, I.e. “We just arrived at XYZ” makes sense on some of the Social Networks but seems a bit out of place on your main Blog page. It can be linked back to and commented on but does not display by default because of the category assignment.
Years ago I used an Asides category for short bits of info that were displayed between posts. When all the custom coding and formatting that made that work fell by the wayside over the years I was left with just the posts. I just added some code to prevent it from displaying on the page, though it still gets found via Google etc. Here’s an example: early aside.
Of course it depends on what you are after. Excited to see where this goes.