Well, I don't know all of them, but I know a number ...
Priest: Temple of your deity (Helm, Talos or Lathander) (Temple district)
Fighter: De'Arnisse Hold
Thief: Thief's Guild (Docks Area)
Bard: Five Flagons Inn (Bridge District)
Druid: Druid Grove (near Trademeet)
As for your second question: no, only the protagonist gets a Stronghold quest. Well, you can do the step-up to each one of them, but except for the one that fits your character, they all stop there.