No guarantees I am afraid. Especially with Windows there are just too many potential gear combinations that it’s impossible to say if something will work 100%. Even on the Apple side of things I’ve been hearing some Traktor problems recently.
That said, USB3.x is backward compatible and should work. These are official design specs and are valid for any USB 2.x device. Clearly there will be always cases of some kind of incompatibility, just not possible to predict for which gear. I have not heard of any specific generic problem in that area though. Then again, I don’t hear everything 😀
Not sure why you’d want to go back to Win7. I am no great advocate of upgrading OS at the first opportunity, but it seems Windows 10 is now stable. For sound I would personally always try using Asio4All drivers rather than the factory ones, but that is just my personal choice.
One thing that you can always try is using a powered USB 2 hub, that way your gear (audio interface, controller) “sees” a USB 2 connection.