Question 1: I used EQ to prove the 12.75 & it's actually 12.728" Not enough to make a difference but could on a king size quilt.
Question 2: That's a personal choice.
Question 3: Don't know about the wool batting. I mostly use Warm & Natural or Warm & White. I like being able to quilt up to 10" apart, although I almost never do that. I use Pantographs on my LA and I quilt much closer seams. The wool batting that I looked up using Yahoo says to quilt 4" apart. That's too close for me.