Just to clarify, the custom characters are only for playable characters and not NPCs. Though it would be cool if a 9th NPC was a customizable NPC who also moves into Silverpine and you can write their backstory for the AI to play out.
From casually playin, there are 8 AI NPCs and 4 are female: Oriana, Celandine, Rosalyn, and Mirel. Rosalyn is an herbalist in Silverpine you'll likely see her walking around at some point. Mirel on the other hand is not so obvious. I didn't know she existed until my 4th night when I just happened to see her by the market stall just before midnight. On her days off, she'll come into town and stay the night at Gareth's inn.
As far as I know there's only Silverpine as a town you can explore, plus a few dungeons in the area. There is some lore for a capital to the east called Thalassar. At the moment, it isn't accessible, so ignore any invitations or requests to go there to visit, fetch, or deliver anything.