At this point, you have a pretty good grounding in R. You are capable of doing lots of things in R. It may be all you need, but even if not, you know enough to ask a question online if you get stuck on something.
The remaining topics are more advanced, and lessons will be somewhat longer and more detailed that the previous ones. But you are still strongly encouraged to go through them, as they will not only cover new topics but also give you deeper insight into the earlier material.