Breathing is easy. Honestly just add tween frame abuse it. Since your doing manual frame by frame animation and not keyframe animation, that really is the only way to do it since it’s such a slow and subtle movement. As for hand to hand, basic movement, punches are typically 1 to 2 frames in length, like always force should apply to the whole body but have the most effect on the point of impact. Missed punches could have a shake to them and should be futher in length with an easy. The shake like a verticle bob is to mimic the muscle tension you get with movements making use of more muscle. You can see this typically when you throw a punch yourself or do any sort of aggressive movement. Also don’t forget anticipation on the recieving end, characters should have a visible reaction to expected punches, this adds complexity to this type of animation.