My DD is interested purchasing a Cricut but there are so many variations and costs. She has many questions that we can't seem to find answers to. Help please. -What are the major differences between Cricut Expression, Cricut Expression II and Cricut Explore. Are there any major features that make any of these models a must have? -Are the cartridges compatible with all the models or are the cartridges model specific? -Are there any other accessories that need to be purchased that are not included with the machine that are necessary options right away?