A mini PCs sips power when they're mostly idle, at about 10/15w then it creeps upwards if you push it. It also only needs the iGPU anyway even if you wanna do trancoding on Plex. It will most likely be way more efficient that a desktop with a GPU on it
I think the best choice is getting one of those so all your services are working all the time. A RPI will work albeit you gotta be aware of its limitations.
I have it running for a couple of months now, doing just fine. Had to change my compose file a while back due to some change but rock solid so far.
I do run Syncthing too in any case