Color video is always better than IR. If you are concerned about vehicle color or other in color details you could focus a camera away from the guard house to capture when the vehicle is under the street light by the highway.
As for the License plate, it would be ideal to configure a camera to capture those specifically. At night you would use the guides mentioned above and purchase a camera with decent on board IR, and then configure it to only capture plates reflective properties. In that set up the plate would be the only thing visible on that camera. So you could support that with the second camera that is zoomed in to where the vehicle would be when it is under the street light.
If you got variable focus cameras you would be able to get them zoomed/configured to work from that soffet to capture License plate details.
Make sure to do research on cameras suited to capture moving LPs.
Looking at those pictures I still think 2 wider angle and 2 narrower angle cameras would do the job. A wider angle on the way in and one on the way out, and then a narrow angle aimed at plate level both in and out.
Make sure to use the light from the street lights if possible, and if not you could certainly get some IR spots to supplement.