sounds like you got it working more or less. i appreciate your patience and diligence with all these bumps. fwiw, i updated the Workbench docs:
https://docs.particle.io/tutorials/developer-tools/workbench/#debugging-3rd-generation-
manually put in dfu mode with buttons, particle debug command halts otherwise
i'd like to get this working for you if you haven't resolved the issue but not in this thread. if it happens reliably (try running particle usb dfu <device name / id> directly), please open a new thread with troubleshooting info as described here
thanks for the feedback 