Howdy!
I had a same, but different thing when I was part of a model train club. They had a small LED TV stuck inside an enclosure that made it look like a drive-in movie screen. My requirement was to be able to walk into the audience area and control the display from my phone.
My solution: put a wifi router without internet connected, setup as DISPLAY_WIFI. Then, I put a raspberry pi onto the HDMI, loaded it with LibreELEC (a Kodi/OS on a USB stick), and connected it to the wifi. Kodi lets me play videos and creates picture slideshows from whatever files you place a folder. Kodi ALSO has an addon for CEC (what lets every Blu-Ray, DVD, and sound bar turn your TV on and off via the HDMI cable) and a remote control app.
I put LibreELEC on one USB stick and used another for all the videos/photos (media). The raspberry pi boots into LibreELEC. I used my phone to setup the playlists and a couple of add-ons.
One add-on automatically started whatever playlist I told it to, whenever LibreELEC was started (in this case, rebooted). Another app was a screensaver that killed the TV via CEC command at a certain time. Another was a reboot command that could be scheduled to reboot the computer at 8:55 am, thus kicking the CEC “turn on” command to the TV.
The “ah-HA!” moment came after getting tired of setting up a new playlist every time I updated the media USB stick. I realized that as long as I used the same number of movies or photos consistently, I could keep the playlists the same playlists by making my media files’ names numbers. I even went so far as to make “club photos” even numbered and “sponsor photos” odd-numbered, which ensured equal air-time. This actually came in handy once or twice, as a sponsor thought we weren’t promoting them as much as our club.
So, with my playlist being “media stick->01.mp4, 02.mp4, 03.mp4, etc.” I could change and update the media stick on a computer as much as I wanted, as long as I replaced the old files with new files having the same name. AND kept the same number of titles. If the playlist went looking for 04.mp4 and I stopped at 03.mp4, I’d get a 10 second message “MEDIA COULD NOT BE FOUND” in the middle of the TV
This has a minimal cost, in the long run. $100 initial investment, per TV. Maintenance is simple, once you know what you’re doing. Using the raspberry pi in this mode is rather like using a video game: grab the cartridge and go, with USB sticks being the new cartridges. If a stick goes bad, put a new one in your computer, fire up the “Create a LibreELEC USB stick” app, and make a new one. To upgrade the app, power off the pi, pull the LibreELEC stick, and then use the create app to erase/reuse the stick. To upgrade your media, safely take it from the pi to your computer and have away at it. LibreELEC is free, so no commercial licensing allowed!!
Hands-on instruction would literally be a 3-hour class, with you knowing everything you need to know done in the first hour.
Just a solution that I came up with.