All of them.
JASN_DE
Those fucking religious nutjobs...
Märchenbuch-Fanatismus machts möglich.
1-2 Spanngummis mit Haken dabeihaben.
You can use quite a number of "underlying" distributions, it mainly depends on what you like (Arch-based ones, Debian-based ones, etc).
As a desktop environment, have a look at XFCE or LXDE.
What are the main advantages to plex?
AFAIK they offer more apps resp. apps for more platforms. Apart from that, nothing really. Maybe a little more idiot-proof.
Und: fliegen oft langsam genug, dass man sie gut fotografieren kann. Wenn man denn mal welche findet.
Debian as a server base OS is well-tested and (for me) ultra reliably stable.
Same here. No idea about themes, but it works really well.
FreshRSS, + Readably on Android. Has worked well for me for years.
That was the first one I tried. Sounded fantastic in theory, didn't work out for shit. For some reason the sensor dropped out constantly. The USB PSU bottom was nice though, no batteries to change.