Pika has it right. I just checked my WM Ultralight, and they used a fairly uniform 10 stitches per inch. The baffles should be folded over so that the stitching goes through two layers of baffle material, IMHO.
A single row for me too. It's complex enough to sew with one :/, and needs as little holes as possible. One or double layers depends on which material is used I guess. I never had trouble with strips of no-see-um baffles, for instance, sewn "flat".