@jbaik and @tkane there was a time when the course actually was structured much as you describe. Unit 3 and 5 were combined in one large unit near the end of the course and Unit 1, Unit 2 Chapter 1 (everything but data) and Unit 4 all came before it. We assumed it made more sense to group similar content.
Feedback on that version of the curriculum was that the long stretches of similar material, in particular programming, started to wear students down. It also meant students ended up waiting a long time to program which was frustrating for some students. This is in part because one of the major stakes in the ground for this curriculum is that we didn't want to start the course with a programming unit. Responding to this feedback led to the current version of the curriculum.
That said, you should of course use the materials however makes sense to you and your classroom. If we start to see evidence that a different order than the current one is clearly better, especially for new teachers, we'll likely switch it at that point as well. For example this year we began recommending that classrooms complete the Explore PT following Unit 4 rather than waiting for the end of the course. Feedback like this is really useful in pointing us in the right direction.
Good luck to you both and the rest of the CSP teachers out there and thanks for taking a moment to share your experiences.