I don’t know enough about DX11 or DX12 to say which should be used. I mean, one would think DX12 would be the better goal, just by the fact 12 is a higher number than 11. But I leave that to the people who know what they’re doing.
With extended support for Windows 7 ending in in 3 months (January 14, 2020), meaning no more updates or security patches, I would have no problem with a move that required Windows 10.