1.- Ok
2.- Mountain? eeee. I doubt it is a kick, it much more seems that he went all over the Gyojin while with Queen it was single kick
3.- If you punch my arm, will I feel it to the bones? Obviously, so is it also internal damage? Mmmm no. Internal damage works from inside to outside. Hits, puches, everthing, you will feel it to the bones.
4.- Its power depends on the durability, while it wastes stamina. Those are 2 different things. Everthings costs stamina, otherwise it will be infinitate.