Running down hill is not as easy as you think, and it takes a lot of practice. Once you get it down and learn how to roll down hill without having to hold on the brakes you can really fly.
I bought cheap pieces of clothing that I could strip off during the race and discard. Gloves and arm warmers made out of long socks. Great idea.
Don't overdress - start the race feeling a little cold. You WILL warm up. Overdressing will make you get overheated and can really affect your performance.