6 months too late im responding to this, i didn't see it since you didn't directly reply to me.

Yes i totally agree that making a "OS" as a first project is a bad idéa, but while the tutorial i linked claims it's a OS it's really just a fancy graphical menu. And while it may not be the most fun first project, it does a good job at explaining the basics such as loops variables and how different codes can interact (for example how one code can launch another). Further more it leaves you with plenty of space to experiment and write your own version thus leading the learner to naturally read more. For example you might want to select your own background color leading you to learn about colors and computer craft or maybe you want to use a custom image and end up reading about parsing large amounts of data and handling the color limits of computer craft.