Hi Animalia,
I dont know the answer to (1), but regarding (2) -- it is good idea to file Eb1a, or Eb2-niw, or both of them, if you believe you qualify. You can file in all three categories if you want: Eb1a, Eb1b (OR), and Niw. Why not file Eb1a and/or NIW now, and after you switch to Dept of...