Well, copying the Install macOS Sierra app to the desktop did the trick, and I seemed to be able to create the bootable flash drive. The Terminal went through the rest of the process as shown on the video, anyway, and the files were now on the flash drive. I installed the Clover UEFI on the flash drive with the settings from your screenshot, and replaced the Clover folder with your version.
Unfortunately, every time I try booting from the flash drive, it seems to freeze up just before the progress bar reaches the end. No more movement, just an interminable spinning beach ball.