#4 - the lightmix is inside the VFB. When I play with lights they don't seem to change. I will try to add some more and test, but just wanted to let you know. If it's working for you then I must be doing something wrong :)
There is an issue in the standalone where the Sun has no effect.
But for each object you can tick the lightmix box on the material tab and give each light a name (or the same name to group them). Only has an effect for emissive materials.
I just did a test and those lights show up and they can be controlled.
The output will be in the <export directory>\render\<scene name>lightmix.png
You can pull that back into Blender for compositing or the individual light renders too for some post render light mixing.