If you are into the "anti-bloat" movement, you might enjoy the "The Cheapskate's Guide to Computers and the Internet" @ https://cheapskatesguide.org/

Exactly the same setup on my machines. Works fine and can be integrated with any other sync programs as needed. A flexible and robust approach to RSS. Newsboat is also a great option, for those who prefer a dedicated RSS app.

This ^

Take a look at Syncthing. Been using it without any problems for a few years now.

This, or resilio sync has been solid for me. There are others like freesync and goodsync but I have never tried them.

isn't media goblin a bit like this? at least for the media sharing bit.....

Very much so. They are introducing federation features, that make these even more of a reality.

I just tried this out on Sandstorm. I have to be honest in that I didn't like the interface. I can only upload one file at a time. I'm looking for an app that can replace G+ photos / posts (but private rather than public). I need to be able to upload thousands of photos and videos.

I also tried out Lychee on Sandstorm as well. Whilst that can upload multiple files at once, you can't organise multiple files at the same time.

OpenPhoto looked like a good option, but I had some real struggles trying to get it to work on a Ubuntu server on Digital Ocean. Not sure what I was doing wrong, but I got some really weird errors that I couldn't get to the bottom of.

The best photo / blog app I've come across is embedded in my Synology NAS system. It's awesome, but without a fibre connection you just can't host photos and videos on a residential internet connection (although that would be the perfect solution).