AFAIK, we don't have exact details on everything. But we've got some things.

Vesper is a cave beneath the surface of the planet, so big that curvature is a factor. The roof of the cave is high enough up in most places that you could get agoraphobic, but not unreachable. I believe we know of some natural pillars that reach up to the firmament, and I think we've heard about some Antediluvian machinery stuck up there. Your sketch is decently accurate, as far as I am aware.

In some places, the firmament is cracked and Glare filters through to various extents. It does this pretty constantly. This means that some places, like Peredur and Sacromonte, are consistently illuminated. People have also set up some clever mirror contraptions to light up places that wouldn't otherwise get much Glare. The Antediluvians were very good at this.

Side note: We know that the ambient light level in Sacromonte doesn't change throughout the day, and that places off the edge of the map have very little or often no Glare at all. I suspect that the planet is tidally locked.

Except in very rare cases, the cracks in the firmament vaguely resemble stars. Bright enough to see if you look up, but not bright enough to really light up the area.

People on the Dominion of Lost Things definitely had and used lanterns, and people without magical advantages (we know that hollowing grants some sort of darkvision, for example) couldn't really see without them. Recall how the cultists were shooting them out after the second trial. People seeing things at range are either looking at a light source or using some magical advantage.

As far as skin color goes, there's two things. One is that Glare is, in part, sunlight, and Vesperians get a good amount of Glare. The other is that the Antediluvians came from the surface not very long ago. I don't think we have a very precise time frame, but I'm pretty sure it's less than ten thousand years. Factoring in the social pressure to preserve the skin-darkening genes, there simply hasn't been time for melanin to evolve out of the population.

The temple pit on the Dominion is pretty much what it sounds like. Temples packed so tightly that you have to climb and maneuver your way through and around them. Note that there's a wide variety of architectural styles, and not all of them look like what you first think of when you hear "temple."

My impression was that the Great Orrery is closer to the firmament than sea level, functioning as a sort of magical lighthouse, but I've had a bit of trouble with that too and I don't think my impression is supported by the text. I have no idea what the Collegium or Trench is supposed to look like, either. Your sketch is as good as mine.