Thanks.

In fact, I had already explored HDRs but seeing as the background never actually resulted in a dome, I felt them unsatisfying. Then I tried out Snarrly's EZDome but found almost no SIBLs. Not being ready to give up, I then installed an app (and very good it is too) to make those SIBLs myself but only partially felt I knew what I was doing.

In most cases, I was never really happy because the HDRI method always proved too bright and awful for any scene where I would want to use Emissive textures. For example, if you check out Polyhaven and the nighttime HDRI, you'll find most are not really nighttime but actually look like dawn-light.

So I went back to regular ground and skydomes, merely modifying the material to provide Emissive light from the dome.

And building Cycles shaders from the ground up.... Hmmmm... As hborre mentioned, Cycles is tricky and I'm in for what seems to be an immense learning curve.
Very daunting all in all.