More than likely, if you are on a domestic inbound, the weather is good, and air traffic delays are not at "maximum" you will arrive at Terminal A. But hey, if you arrive at Term C, and are making a connection out of C, you just saved some time on your conneciton, and can walk to your next flight

Yes, all concourses of Terminal C are connected via the "airside corridor". A bus operates between them on the "sterile side" The bus leaves from near the throat of the C-1 concourse Gate C71 (see the map) and at Terminal A arrives next to gate A28. There are many a posts maligning the bus (or the people checking your boarding pass before you get on) but.....It is what it is. I've never missed a connection because of the bus itself, but you will have to do stairs at both ends. there is an elevator at both ends, but it is slow enough that I have never waited for it. You do get an up close and personal view of the ramp activity

There is an elevated monorail that goes between the rental car station, terminals, parking lot, and the train to NYC, but it is not on the "sterile side" do NOT take this unless you really enjoy interfacing with your friends from the TSA (clearing security again)