Here is the end result of working on the custom user interface, created using Photoshop, Flash and Kismet in UDK. In terms of functionality, the play button launches the "DM-Deck" map in UDK. The Options button jumps to a new window where all functionality is off, forcing the player to play as we make it for now at least, and can only press the "Back" button to return here.
I am now confident i know how to get the custom user interface to do almost anything i can think of, as i already know Flash and some ActionScript, and camera controls seem to work in UDK now. Indirectly, this has also given us an insight on how we would make a custom HUD (although we don't plan to have a big HUD anyway, maybe just a map which this doesn't help with).