For this purpose maybe an Arduino Uno with an Ethernet shield and a 2 or 4 line LCD screen would be the most reliable solution for the slave side. A display you could talk to using the standard library https://www.arduino.cc/en/Tutorial/LiquidCrystalDisplay
These displays are easy to read and mount to some enclosure for tidyness. The Ethernet shield equipped Arduino could then subscribe to a MQTT topic to listen for the messages.
Edit: I missed the display requirement. That big displays might require a Raspberry Pi to drive them. So maybe just one of those small monitors used as a standard HDMI display. A Raspberry Pi 3 would be sufficient to run a simple Node-RED dashboard on the slavs side to display the messages fullscreen.
