13% of us sleep on our stomachs.
This is not the best position to sleep in because your spine is not in neutral alignment (your neck remains in a twisted 'torticollis' position through the night. At best, a tummy sleeper should sleep with a much lower profile pillow than back or side sleepers. You're going to need a much lower profile (loft) pillow than say, a side-sleeper.
Onto Question 2, then you're halfway to your unique Pillow Number.
