Wow, there's a lot of useful info there...and I'm sure it will all be necessary. I've experienced the scene going black thing, and wondered okay, I added a light, and it went black...haha.
With Studio, as soon as you add your first light, the entire scene will react to it. So when you add a spotlight or pointlight with default settings, the light is sitting on the floor... therefore anything else is dark. That's why it happens. But if you start by adding a distant light first, then the whole scene lights right up.
I start with the spotlights first because having the rest of the scene dark actually helps me figure out where the light is actually going when I switch back and forth between spotlight views and render angles to check things.
[Edited to fix my typos and clarify]
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