The pit calculator is designed for a horizontal offset so I don't think it'll be the same for a vertical. I don't know of any calculators for a vertical.
Ditto.... you are on your own if you build a vertical. Remember that heat transfer is much better as the heat source is directly below the cook chamber and therefore allows the firebox to smaller than that on an offset. To allow you the control you need, many people decide to install a slide damper on the throat to help control the heat input.