Just throw in plenty of hill training & you'll be fine. And some off road races or training, trail or fell, so you get used to the ground being uneven.
I actually wasn't cold at all last year. I found the Bog of Doom surprisingly warm. Well, maybe not warm, but it wasn't that cold. All depends on the weather of course. It wasn't icy last year.
It's just a good laugh & the atmosphere on the start line is exciting.
Don't go off too fast, as most of the hard stuff is in the second half.