I don't have MW5 installed anymore but from my memory you can assign a weapon to multiple firing groups. The only thing I think they did remove is it doesn't use a select fire active group button anymore.
Yeah don’t care about motion controls, those are best left to standing games.
Not sure if you have tried it but VTOL Vr may change your mind on that. It will never beat HOTAS but its far more immersive than relying on your keyboard or controller.