So a couple of years ago I first upgraded to High Sierra and then installed Windows 10 on this Core 2 duo iMac and everything went more or less smoothly. I was able to find all the drivers from bootcamp download and the only issue I had was that display brightness control although would move up and down but wouldn't actually adjust the brightness. However I was also able to fix that using windows registry tweek by adding DWORD=1 somewhere for brightness control.