I see no one from N90 has chimed in yet, but I can answer your first question with some degree of certainty . . . In a big TRACON like N90, C90, SCT, etc . . . a controller is assigned to an 'area' within the facility and certified in all of the sectors within that area to become a CPC. A Big TRACON might have 5 or 6 areas with 6 sectors each in them. SCT's areas are set up around the bigger airports, like BUR, LAX, LGB, SNA, and SAN.
And this exactly matches NCT from the tours I've had there. NCT is actually set up like a bicycle wheel: spokes on a hub. Each area is around the center, and controllers control sectors in that particular area. The controllers there get certfied in each sector of that area, so they can rotate throughout the sectors in that area, and throughout ecah area in the TRACON. That way, controllers are interchangeable.