Neo38m,
did I understand you correctly that you currently have an image of the NUC? And you want to push (i.e. restore) that image onto the other NUCs to avoid installing them from scratch?
If so, I have seen there are/were some issues using external/USB WD disks on USB 3.0 ports but at this point it is not certain was it due to WD drivers, or USB 3.0 host controller drivers.
If you say the USB disk is working before you start making the image, there might be an issue with your imaging software (if Windows detects and uses the drive properly). Which imaging SW did you use?
Anyway, I would advise you to check this fine article on MyDigitalLife, and use the Macrium Reflect disk imaging software (free edition is enough) in combination with WinPE (Macrium Reflect can create the WinPE rescueCD or ISO, or make an bootable USB stick, and you can then integrate the required USB driver(s) into your WinPE boot.wim using the info provided on the mentioned link).
If you're using USB3.0 devices, an added benefit is that the image restore procedure described on this link will enable you to work with maximum USB 3.0 speed.
I have tested this procedure (albeit using WD external USB 3.0 drive and D54250WYK NUC) and can confirm it is working - i.e. image restore was successful over USB 3.0 port. You will need to check/investigate which USB driver files to integrate into boot.wim though - but once you do that, restoring the image on the other NUCs should go fine. I would recommend to integrate your NUC's Intel USB drivers (and possibly the WD drivers, although that should not be necessary).
A bit off topic, but - when you installed the drivers on original NUC (i.e. the one you're imaging), did you install them one by one (rebooting after each installation), and beginning with Intel INF files, then Intel ME driver first?
Also, if you're managing a school LAN and have a DHCP server and a NAS hooked up to the LAN, you can even put the NUC image files on the NAS, integrate the NUC LAN drivers into the boot.wim using the above procedure, and then just download the image from NAS. This can take some more time to get it working but it could save you some serious time on image restoring; Intel usually provides the WinPE LAN driver (at least for D54250WYK), however I was not yet able to get the LAN working inside WinPE (but then, I have only 1 NUC so I don't mind using USB).
Regards,
/HarveyV