I would recommend getting the custom courseware. The main points of each lecture are outlined and some important slides are given. I used it as a guideline for my own notes. Generally, what the prof puts in those little bullet points and slides are the most important points, so it's great for knowing what things to focus more attention on. It also has some questions at the end of each lecture to get you thinking about the material. That being said, there isn't really any information exclusively in the courseware, so I wouldn't say that it's essential, only that it's useful.
However, I would not recommend the textbook. I really regretted buying it. It was just all the same concepts, with nothing new, paraphrased. If you feel that reading the textbook will really reinforce what you learned in the lectures because you're that kind of learner, then go for it! But in reality, most people that I've spoken to don't end up using this textbook at all.
Hope I was helpful!