@Anonymous, below is an image showing how I would probably break up the rocket. Each color is a unique sub-assembly which can be re-used multiple times.

The basic breakdown is:
- Bottom section with fin (red) - 4X
- Bottom section with hole (yellow) - 4X
- Middle section with hole (green) - 7X
- Middle section with entrance (blue) - 1X
- Upper section (purple) - 8X
As for the modeling itself, I would personally use multibody modeling. You can google this to look into it.
That's just how I personally would do it after a quick digest of the overall assembly. Other people would do it differently and no one way is "the right way". But some will likely be better than others (including mine) for your application.
I'd be curious to hear if others know of a good parametric way to pattern the decreasing sizes of panels in the upper and lower sections. The middle one is easy, just a pattern of the same panel. But the top and bottom may be a little trickier.