Get acclimated to the temperature early tomorrow. Splash around and be sure to put your face in the water. For some reason that makes it easier.

b) any tips on how to keep myself warmer?
Two things, one counter-intuitive, one gross-sounding, but 1) let a little water into your wetsuit beforehand. The wetsuits are designed to work with your body heat and trap warm water inside. 2)Pee after you start the swim. Sorry. Everyone else will do it. You will be swimming and you'll go through a warm patch and guess what? That's not a warm current that you just swam through. Do it early and you'll be plenty clean by the time you get out of the water.

You will likely warm up during the swim, and high 50s-low 60s are way warmer than 47.

Are there going to be waves or is it a protected area? If there are waves and you haven't gotten through them before, have someone show you how to dolphin-dive. It's easy and kind of fun, and will save you from anxiety when you are trying to get in. I know, nothing new on race day, but this might be an exception if there *are* waves to get through. This site has a good description of it, but you should try it as well: http://www.hulaman.com/triathlon/open_wtr.html

Relax and have fun - good luck!