I've now got a Python webserver up an running (on my Linux server, for now), which offers a list of modes for the user to select from. When a mode is selected, it uses jQuery to push this back to the webserver, which then tells the other thread to change which animation it should play.
It's on Github, obviously - https://github.com/thejpster/xmas-web.
The letters have arrived too, and I had to re-jig the LED layout a bit. It was tricky to get something that lines up in nice neat rows, but I think I got there in the end. After a few goes on the computer using LibreOffice Draw, I decided to just use chads from a hole punch to get the layout right.