Hi, great post. I am trying to make a set up like this, only instead of the Attiny I thought of using an arduino nano (although I just found out the arduino micro pro should using less power during "sleep").
I understand you only want to make pictures at night, as you are using the LDR5516?

Is there a reason why you directly connected the 3.3v power to the PIR sensor?

Furthermore, you complain the first picture is black, but in your setup you do have the focus, which should wake the camera and the flash (as far as I understand at this point)
I was thinking to first sent the focus signal, and then shortly after that the shuttersignal so the first picture will already be ok (but I have to test this as soon as my stuff arrives)

I will be using a Panasonic lumix G5, I have it already a long time and if it gets stolen, well too bad but no problem.
For the box I will be using a airtight food container which opens from the top, 4,5l so I hope it will be big enough.
Last question, I am very interested in the STL files for the 3D printed parts, can I download them somewhere?

Thank you for all your work and information here, very convenient and interesting.