In reply to item #1 above,
L/N 968 The prototype -400F was built for Air France and first flew in 5/93 but was never delivered (allegedly due to the refusal of the AF pilots union to fly a 747 2 crew) and was stored in Marana until delivery to Cargolux in 9/95.
The first commercial operator was Cargolux who took delivery of L/Nos 1002 and 1003 in 11/93 and 12/93.
Atlas received their first aircraft, L/N 1165 in 9/98 some 5 years later.
None of the first 3 aircraft, including the prototype has or ever had the stab tank activated in commercial service.