Yes you will need a level shifter to go directly to the pi pins, this is my shopping list:I can, but give me a few days. I need to get into the top cupboard to get to the panel. Thinking about it today, I actually want to do away with the usb serial port and wire the Pi Zero Uart directly to the panel (they both 5V ttl) and print a nice enclosure for all of it to fit into. It’ll make the setup less clunky. Pi Zero, Panel, klaar.
Edit: I see Pi’s pins are 3.3v and not 5V tolerant. Crap.