For the 1mm diameter, the images were too dark as not enough light was coming in that our iPhones were capable of picking up (unfortunately we weren't able to procure a digital camera in time, but we did install a Slow Shutter Camera app that mimicked a long exposure pretty well!) Another side effect of this was that the images had barely any color, so we were effectively only able to capture silhouettes of objects.
For the 3mm diameter, the images were still rather blurry but we were able to capture more color. As you can see, the blue in the sky photos is much more vivid here than in the 1mm pictures.
The 5mm pinhole performed the best for us, given our setup (long-ish length of box, and iPhone with not as much resolution as a digital camera). The colors were the most vivid here, which makes sense as there's more light entering the box. Surprisingly enough, the 5mm photos show an even better resolution than the smaller holes, which goes against our intuitions that the smaller pinholes would work better.
Perhaps the reason why the smaller pinholes didn't work as well for us is because the iPhone has a smaller aperture compared to larger professional digital cameras with massive lenses.
We used an old shoebox. Pretty self-explanatory. Did the job.