I am currently running Whiterock. Based on the character classes and races, the players and I sketched out a very brief background for each character. In running a campaign, I like giving every character a mini quest or goal of why their character is out and about and what brought them to Cillimar.
The strife between the Warland refugees and the Noble populace is a rich with background possibilities.
The strife between the Nobles and The Government of Cillimar is good too for story. I have pegged the root cause of this as Cillimars sudden growth with the gold discovered around Cillimar, and Cillimar itself getting the concessions of these mines from the King instead of the Local Nobles. Add a new open immigration policy of the Kingdom (all the Warland refugees), the influx of population, cheap labor, and the power it represents, you get an old guard (some of the powerful nobles) that are really feeling disaffected and Jealous of the power that the merchants, guilds, and city government have suddenly got.
I have 10 Players. Four I gave 'warland refugee backgrounds' in one way or another. Mind you, what you see is what you get. This is the background of the character going into the campaign, brief and open-ended to build on later as the game develops.
Here are two sample backgrounds:
One is a street thief working the Kings Gate area. Her parents got taken by slavers on the way to Cillimar 1 year ago, and she was the only one who escaped. She found a family in the Thieves Guild of Cillimar. She has a burning hatred of slavers.
In the first dungeon level (2nd level in game) the party found the accounting books of the Duegar Accountant. They learned her parents and friends had been sold from that.
Another Character came from a noble house in the warlands, whose entire family was murdered one night long ago. He was spirited away as the attack happened by one of the servants. He remembers a couple of faces from that night and a symbol. The servant raised him and trained him as his own, teaching him skills no servant should know. The servant eventually dies, and the character goes to Cillimar because he has information that the organization that killed his family might be operating in Cillimar.
I had no idea about the organization that killed his family, nor the servants background. Some of that has started filling in. The organization that killed his parents was a group of assassins known as The Creed, and in researching them he has found out that they may have had a hand in the starting the strife that is now the Warlands.
The characters in the dungeon have 'cleared' the slavers, The Orc slave buyers, the Whiterock Orcs, and are starting on the Troglodyte level. They made a trip down to the watery level with the Duergar, and with information provided by Lady Talbusk of the temple of Justica, found and cleared the Sundered Scale hide-out.
I started small with Cillimar. I have only brought the NPC's in as I have needed. I did not want to 'overwhelm' myself with all of them. If I could not remember one, I just made one up and have used it.
I have tried giving them good reasons for going to Whiterock (one of the Characters, a Dwarf, Great Great Grandfather was part of the Deep Earth Mining interest that mysteriously dissappeared in Whiterock. He considers Whiterock his by hereditary rights, since the DeepEarth mining interest was the last to 'own' Whiterock). So far it has been really Fun. I started small, and have kept the plot manageable. The players also come up with great stuff to add to the backgrounds and adventures by their actions.
The first adventure was nothing more than the party Ranger (native of the farmlands around Cillimar) had contacted each party member to hire them for hunting some Goblins. He had scouted out a new nest of Goblins that had moved into the area. Because Cillimar cannot afford a standing army right now, they have gone to bounties for enemies of the state. Goblins and Orcs are basically 2gp per head. That is basically a hard days wage around the area. It creates a great market, helps cull the vile humanoids that infest the southeast of Cillimar.
From that adventure, a farmer southwest of Cillimar approached them and complained about strange howls and gutteral language being heard from the swamp to the east of his farm. The party investigated and found a small slaving ring run by a jailer in Cillimar (later on, through investigation, they found was associated with the Undertaker). They also found out their where slavers in Whiterock, which for various character backgrounds they felt they had to investigate...
Start small, keep it manageable, and only bring those NPC's in who help advance your groups story.