Event looks good. I do marathon and done a few triathlons, going to take the tris more sereiously next year.
My advice for the run would be, listen to your body, if you feel like you need to slow down, then do. Likewise if you feel like you can push then do. You'll be surpirse what your body can do, most of the pain etc will be in your head. but my biggest peice of advice would be don't walk, if you lose rythem is over, when you walk your muscles will tighten up as the latic acid will settle in your legs.
Also dont do anything different on race day then you have done in training, people on the sides might be handing out jelly babies etc, dont eat them if you dont know how your body will react. If you can practice taking on water when running, that may help. I remember the first time I went to an event and just picked up a bottle of water, i drank half of it then spent the next 5 mintues throwing up on the side of the road. That was during Notingham marathon a few years ago.
Go onto www.realbuzz.com loads of training advice on there