It's late in the challenge, but even then, I think it's interesting and useful information to share with you 
The two posts below explain alternative boot modes for the Raspberry Pi 3: from mass storage device and from network!
- https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/
- https://www.raspberrypi.org/blog/pi-3-booting-part-ii-ethernet-all-the-awesome/
I think the network boot looks particularly interesting! Maintaining a single repository containing all your files and tools, ready to be deployed on any Pi would greatly simplify maintenance and control.
Perhaps not for this challenge anymore, but I will certainly be trying this in the future
