2. If necromancers are a known element of society for long enough, then the opinions of the general populations will get interesting. Do they resent the necromancers? Do they admire them? Do kids want to be necromancers when they grow up, and if they do then what do their parents think about it?
Well it's still the basic Dresdenverse setting where magic is a secret, so I wouldn't exactly call them a known element of society.
3. If necromancy remains established in the city for long enough, then it seems inevitable that some sort of subculture will form. So, do necromancers have bars? Do they have a common system of training new necromancers? Are they united socially against the Council?
I don't think they're going to end up too sympathetic here, since when my players did their background stories two of them essentially went, "And there were these bad guy necromancers hurting people, so we kicked their butt". And to be fair, it is somewhat of a soul-twisting form of magic. The section on necromancy in YS isn't that extensive, but it specifically lists human sacrifice as falling under necromancy.
That caveat aside, there's definitely going to be a subculture. I am liking the idea that there are a few 'big bad' necromancers around who have studied the lore of Kemmler, but there are also guys like the taxidermist who just do it on the weekends and such. They might not have bars, but they do have lodge meetings and apprenticeships, and some sort of exchange of knowledge.
What I am currently trying to struggle with is ghosts versus souls. Okay, so ghosts are echoes and not people. But are there cases where the actual souls of people hang around? Are there cases where necromancers call up actual souls/dead people from Beyond (and not just their ghostly echoes)? The whole 'guide to the dead' bit the Son of Hermes PC is interested in is predicated on him actually helping dead people reach their rest, not just echoes of dead people. How do I handle that? Are there echo-ghosts and then true spirit ghosts?
I am also trying to figure what necromancy does other than zombies. Let's do away with zombies or anything zombie-related for the moment. No reanimated flesh. What other things fit under the thematic reach of necromancy?