I know there are several threads on the forum about building custom modules. You’ll likely need to add support for you custom module to the firmware, and flash it. There are instructions for building, packaging, and flashing your self-compiled firmware.
You do need a toolhead attached for the machine to operate, but I don’t have a 2.0 to test hot swapping (#1 and #2). #3 is not a dedicated pin. The 2.0 uses canbus, and sends messages to the module, and the module replies.