You shouldn't do this if you want your cookies to taste like cookies. Isomalt doesn't taste as sweet as the table or brown sugar that you would typically use in cookies.
Pour boiling water into the container, leaving room at the top. (If your candle is made of a soft wax, such as soy wax, you can use hot water that's...
Sure you can! You can use a variety of essential oils to do that, but make sure you're buying candle-grade oils with the fragrances that you wish to add.