A little note that might help.
Be careful of the USB key you use. At first I used a 32gb key, recognized in windows as mass storage. In Rufus I've had to use ALT+F combination to recognize the key. When you try the procedure with such a device, it fails : the installer format the usb key, not the tablet disk, and can't deploy the W10 image as the source disk has just been formated :-)
I just tried with a more standard 8gb key, works like a charm. At least the first step of the procedure, currently I'm at the W10 preparation process.