This is new to me too so why not the blind lead the blind.
As I see it you first should have a light source in the model. Attached are my settings for a Lumanince that was assigned to a sphere. The location of the sphere doesn't matter. It is also set to (7) Load to render lum only , so the sphere is invisible.
If you set (5), Altitude and Azmuth as I have set (18-120) the Sun will be 'low and right' Early morning, based on Plan View , up being North. (6) settings will give you a clean hard shadow. Shadow Transparency 'ON' let Sun in Windows (through glass).
If the side you are rendering is difffernt than mine the (5) settings will have to change. Azimuth is based on Zero = North, 90 = East , 180 South, 270 West.
Do a Quality render to check Sun position.
What I did next is a simple Final Gather, I didn't mess with the Style Manager. I liked Standard 50m (3) (Presentation took much longer without significant improvement. Uncheck all at (4).
That's all I know.