The sliders for light intensity and exposure are indeed working the same way – till you have just one light source. With multiple lights the intensity changes the power of just the selected light, while the exposure has an overall effect. It is true to the metaphor of powering up and down the individual lights, and increasing/decreasing the exposure.

The matte/shiny slider regulates the quality of the surface. Matt reflects just the diffuse light. Shiny material reflects also the specular light. On the other side, the plastic/metallic slider regulates the way how the light interacts with the material. Plastic just adds the color of the light to the color of the material, metallic multiplies the two colors. So if you shine a white light on a red surface, if it is plastic, the highlights end up pale red. The metallic surface has highlights of the surface color – bright red in this case.

You also missed an interesting part of the plugin (as it was not really usable for your example image) – the texture channel. You can set it to some of the color channels or masks and it will render as a 3d texture realistically lit by the setup lights.

I have been watching your videos for a long time and it has always had something that was new for me. Thank you for the work. And all the best in the New Year!