Perhaps use any ARM or x86-based hardware that you can put a copy of KODI on. Should support:
a) KODI
b) NVENC/H.265 decoder
c) 4K
d) optional: USB for HDD
e) wi-fi
f) optional: ethernet
(there's so many on Amazon you have to look close... I'll do a quick look after I post this. BTW, if you don't have 4K videos you don't need a 4K media device. very few 4K videos out there)
Then you go into KODI and point it to the proper folder and it will add pictures etc for the movies or even TV shows it finds.
I actually use a WDMYCLOUD which is plugged into my router via an Ethernet cable. So it always is connected and accessible by every PC or media device (though BluRay players that have this capability will not play some 2013+ movies..possibly some earlier ones, as they've started to add a Cinavia audio watermark.. it's built into the BluRay machines from 2013+)