Hi, Susan.

Yes. I believe Level C will work best for your son. The first 7 or 8 lessons in Level C Second Edition are review lessons that will help him learn how to use the manipulatives and strategies taught in RightStart Math. The next 20 or so lessons will focus on addition strategies for both mental math and for trading (carrying). Your son will not miss anything. If you find that he is struggling on a concept, you can linger on that lesson for a day or two. However, if he is adding well, just keep moving him forward. There is no need to slow down, he already has the skills he needs to continue.

The Second Edition uses all the manipulatives in the Math Set. Here is a link to the Math Set: http://store.rightstartmath.com/rs2-math-set/. You can look through the set and see what you have and what you will need. As I don't know what you have, I can't create a list for you. But hopefully, looking through the set, you will see what you will need.

I hope that helps! Of course, if you have further questions or concerns, please do not hesitate to either repost them here or email me directly at Rachel@rightstartmath.com. I am always very happy to help!

Have a wonderful school year!
Rachel