So for example, if I want a spot light, I model in Blender a round sphere inside a circular reflector, apply the Iray surfaces to it, and I have my light. And you also apply much more realistic surfaces to your other objects to that light reacts more accurately.

Kind of like in the real world, where a light bulb is a physical object with a round surface that emits light. With any of these PBR's, instead of adding a standard light (point light, sunlight, spotlight), you instead build a mesh object and apply emissive surfaces to it. Keep in mind, however, that you will probably want a really nice and very powerful graphics card and lots of RAM in your machine. IF your interest is in realism, then it's probably the best and easiest route. The results you can get with Iray are, IMO, pretty stunning, even with stuff right out of the box. It's called a 'physically based renderer', like Octane, and it more realistically simulates light sources and how light reacts in the real world.

But it's free, and DAZ Studio is also free. It's a rendering engine, much like Octane.

Iray daz3d