Definitely make sure you are in the transition zone before they turn up. Have a huge, massive warm coat + some food to pass to your partner when they come in (assuming you haven’t eaten all the food :)).
As you said you haven’t trained too much, make sure you ride within your ability and make sure you hold back some energy for later in the race. I’ve done a few solo races, and would say that a 2 man team can be quite a tough challenge. This may sound super harsh, but from the sounds of things, you won’t be competing for the podium, so the most important thing is to make sure you have an enjoyable time.
Definitely get a plan of what you are going to eat between laps, and set alarms to remember when to get back to transition – the time will go 10000x quicker than you think it will, and if you miss your partner at transition by a few minutes, they might as well have taken it easy during the lap (+ they will be moody with you!).
Have you got someone coming along for support? Despite what you might think, it’s incredibly fun supporting someone doing an event like this.
Finally, saw your post about Bacton Woods and local riding – I live in Norwich, and always out at the weekend/mid week on rides, if you’re looking for someone to ride with 🙂