Pete, thats a very god start. If you want your verticals to go perpendicular to the horizon, you need to adjust the len shift value in the physical camera. When I was using VfSU, I would start with about 0.1 for a shot from ground eye-level. Quickest way to get this right is to tick the material override and reduce the render output size whilst you test out which lens shift value gets your verticals upright.