Is it true that a steward or stewardess was always a member of the crew ?
No. A cabin crew member was never carried on the 747 freighter although one was carried on the earlier 707 freighter.
G-KILO was operated by standard 747 crews. One could operate to JFK on a passenger aircraft and then return on the freighter.
G-KILO operated mainly LHR-JFK. It was sold to Cathay.