Infinite looped shape without loopOut;

I'd say I'm an intermediate user. I imagined this project to learn, but it's proving to be way more difficult than it seems.

I want "infinite" stars (5 point shape layer) to pass through the screen from top to bottom at a linear speed. No easing. I also want the repeats to start before the first one finishes, so at any given time there's a handful of shapes on the screen. Like a steady flow of stars moving downwards. 

I was hoping to achieve this using some expressions so I could adjust things after I built the project like how many shapes pass through, or the speed they travel (by adjusting the start/end positions to be further out)

The first obstacle for me is this: How do I get a shape to travel through the screen over and over without precomping it (and therefore not being able to use loopOut). - the reason I don't want to precomp is so that I can add the other shapes and have them get their time from other shape layers, which is another reason I can't precomp to a specific number of frames. Another reason I don't want to precomp is so that I can adjust the timing more easily.

Thanks in advance for your help. I hope I haven't confused the issue by overexplaining it.

- One idea I had, that may have potential was to set up a very controlled CCParticleWorld to spit out one shape at a specified rate along a specific vector, but I don't have enough of a grasp of that effect yet to see if that's possible