Thanks for posting the updates. If OSPi turns out to be insufficient at powering RPi 3, my suggestion is to power RPi 3 directly with a microUSB cable and USB adapter. Generally it’s fine to have the system powered simultaneously by USB and 24VAC. If needed, you can remove the PTC fuse on OSPi, so that the 5V output from OSPI will be disconnected from the 5V from USB.