A work colleague of mine would give me his Xbox one S. But I'm not sure if I can play with my Razer Viper mini and Huntsman elite. Or do I have to buy new hardware?
No problem you can just plug it in
Yes you can continue to use it. It doesn't matter which mouse or keyboard you use, it just has to be compatible with the mouse and keyboard.
OK. What I forgot does it also work with my headset? And is 7.1 sound or do I have to make do with stereo. (Never had a console)
Of course, just plug the headset into the controller. Unfortunately I don't know anything about the sound. So far, I've only used stereo headseats