* Normally you wouldn't open the RevPi Core case and solder stuff to the base board, though you're given all the information you need if want to do so. The expected use is to just mount the RevPi Core on a top hat rail and extend it with I/O or gateway modules via the PiBridge connector.
* It's either the Compute Module 3 or the older (cheaper, slower) Compute Module 1.
* The schematics of the base board in the RevPi Core are open source: https://revolution.kunbus.de/download/1803/
* Normally you wouldn't open the RevPi Core case and solder stuff to the base board, though you're given all the information you need if want to do so. The expected use is to just mount the RevPi Core on a top hat rail and extend it with I/O or gateway modules via the PiBridge connector.