While we could tell you all the answers by doing the research for you ourselves, the purpose of your project is to not only learn the answers, but more importantly to teach yourself how to find the answers.
You now have some good leads for the next step, so as Ms. Frizzle says, "Go ahead: take chances, make mistakes, get messy!". And with a chocolate project, hopefully even your mistakes will be both edible and yummy!
I just did a little chocolate project with my 4-year-old son the other day. We put some chocolate in the oven in a little mold and watched it melt, and then put it in the freezer, and finally ate it! A simple experiment for a little guy. (He never tires of baking soda and vinegar...)