I fixed my issue. Not complicated but trying and trying the policy of small steps and continuing to scour the internet for info I found the following process to let me partition and install WIN 10 successfully on my High Sierra 2014 MBP
- You need a windows computer to install and use the Windows download tool from here:
https://www.microsoft.com/en-us/download/windows-usb-dvd-download-tool which will allow you to download a installable copy of Windows 10 (both Home and Pro are supported!). Trying to get an ISO file from the WIN site did not work for me as the downloads always failed and with the WIN tool you have a full copy of WIN on the stick that you can keep to install WIN 10
- Using the WIN download tool from a WIN computer, install a WIN copy on an USB stick (min. 4GB and clean). Don't download the WIN 10 Creator Version, use the WIN 10 anniv. version
- Now transfer the stick to your mac, start bootcamp assistant and with the WIN stick in your mac download the WIN support software from the toolbar ACTION menu item to the stick. It only worked for me using the ACTION toolbar item, NOT the menu item in the main BC screen!!
- Once the support software is on the stick unzip it if it is in a zip folder and copy all items from the unzipped folder into the USB root directory (other wise bootcamp will not recognize the software and won't let you continue the install process!)
- Delete the zip and old now empty WIN support software folder
- Now use bootcamp to partition and install WIN on your mac. ONLY check the third and last check mark in the second BC screen to install WIN. UNCHECK the first "create ISO file" and second "download WIN support software" items.
- After this continuing to the third screen I was able to partition my drive and successfully install WIN 10. Have your product key ready to enter.