As far as remember, you do have to "accept" the Google terms, even if you skip connecting the device to a Google account. That's probably because the Google Services are already installed in the Stock ROM, whether you want to use them or not. It's been a long time for me though ...
That being said, the only point with enabling USB debugging in Stock Android is to trigger that initial reboot to the bootloader, which you can indeed also just do manually with the "Volume Dn + Power" combo.
While there really is no special trick about it, let me try a step-by-step:
Power off the de