Sorry for the delayed response to your question.
I assume that your Surface 3 received the OTA firmware upgrade that went out a few days back?
Have you had any luck with the install subsequently?
Microsoft dropped the ISO for 10162 here
http://windows.microsoft.com/en-us/windows/preview-iso
Which you may find to be a better overall option.
Generally, whenever I have had an apparent hang at any point during an install, whether it be a custom clean install or an in-place upgrade, I've found that the culprit is usually bad media or a bad ISO from which the media was created.
And in every instance, when I've re-downloaded the ISO and reconstructed the media the installation has proceeded successfully.
Hopefully it's something as simple as that.