Is there much in the way of security checkpoints between terminal A west/east and B/C? Really want to get off plane and to the right gate for connecting flight ASAP. (this is assuming the first flight is delayed which, apparently it is 45% of the time!)

Coming international but clearing immigration in Dublin and bag will probably go all the way through. Will I still need to go to customs when the flight from Dublin arrives and before I connect? I know I sound like a right idiot, but what's the difference between customs and immigration? On the Dublin airport website, it claims that the US preclearance includes customs, immigration and agricultural inspections all in one procedure...so I'm not sure if that means I'm off the hook when landing in PHL regarding having to queue at customs.