Regarding the linkage between the Shadow War and the Earth Civil War, it seems to me that they were pretty well intertwined up until "Severed Dreams"/"Ceremonies of Light and Dark". At that point, the Earth Civil War kind of fell off the map until "Epiphanies". When I was first watching the show 10 years ago, I was kind of expecting the fact that Earth was an ally of the Shadows to be more significant in the Shadow War in late Season 3 / early Season 4, but oh well, it's a minor thing.
Regarding the Shadows having a "face", I'm actually quite happy that we didn't get to know any of the Shadows personally. The Shadows and Vorlons are supposed to be thousands of years ahead of the younger races. Their thinking and their personalities should be as alien to humans as modern human thinking is to cavemen (or even as human thinking is to slugs?). I just don't think a human writer could convincingly pull off portraying a Shadow as a fully fleshed out character.
Yes, we've got Kosh, a Vorlon, but he was written so cryptically that I don't think this was much of a problem. We never really got inside his head. (This is a minor complaint I have with the Technomage Trilogy, which occasionally tried to take us inside Kosh's head. Not sure that I really found it convincing.) Anyway, the bottom line is that I have a strong preference for SF that doesn't try to humanize super-advanced alien races. I just don't think it works very convincingly. (Same logic applies to the Borg, and it's why, while I think First Contact is a fun movie, I really dislike the idea of a Borg Queen.) IMHO, what works much better is when the super-advanced alien race just seems like an unstoppable force of nature, that follows a logic of its own, that we puny humans can barely comprehend. And I'm glad that that's the direction JMS decided to take with the Shadows.