I use http://fhem.de/fhem.html as basis for my home automation. Right now many of the resources are available in german and I have no idea how strong the non-german speaking community is.
I am using home assistant… it is a home brew system which means its not tied to a singe ‘standard’ like zwave, zigbee, hue… you can mix and match
It can run as a linux VM, on a pi, as a container… etc
You configure it by writing yaml files… not hard but sometimes tedious…
As for plex integration… the home assistant software can track just about any kind of device… I run my main screen plex on a rasplex box…
It all works through a web interface and you can see all your plex clients and what they are playing … they show cover art/poster and you can pause start the streams from there as well…
Limited really by how much time you put in customizing…
I wrote the scene so that when the sun is down and the pi is playing… it dims the lights to ‘movie time’… it it pauses or stops… the lights come up to ‘intermission’ lighting… works pretty slick…
There are plug ins called homebridge… it allows integration with siri … so I can say turn all living room lights to 30% and all 3 lights on 2 different dimmers come up to 35%…