Personally, I would just stick with windows 7. Aside from all the crap that windows 10 adds, its really annoying that auto-updates is always on. I like to turn my computer off, and there's nothing more annoying that turning your computer on only to discover that windows downloaded updates and now has to take the next 5-10 minutes installing them and rebooting a dozen times.
The dx12 issue isnt an issue. most games arent evening using it right now, so youl be fine for more than a few years by sticking with dx11.