Regardless of what the final version of my first backpack includes for the Arietta G25, I thought I'd share what I plan to use as a template to start this design, and hopefully others in the future. If you download and open the template, you'll see a section of the schematic that contains a map of global net labels for each physical Arietta G25 pin. This should help make it easier and more straight-forward when you decide to plunk down a I2C device for example. In this case you can just place the schematic decal and connect the SCL and SDA to the intuitively-named global nets for the Arietta G25. This is in contrast to having to go back and forth between your schematic and the Arietta G25 pinout documentation here to figure out that PA31 -> SCL0 and that PA30 -> SDA0.
Read more after the break for pictures and to download the files from our github repository.