I think role="slider" is more semantically appropriate. "scrollbar" typically deals with moving through a view, while a slider moves through values -- which is closer to what we're doing. 

With that you won't need aria-orientation, but aria-valuemin, aria-valuemax, aria-valuenow, and aria-valuetext are nice to help keep track of the values.The first 3 are number values, the "aria-valuetext" though, allows you to put a little more description to be read when the item is selected.