Are you getting the Basic Weight (BW) and the Dry Operating Weight (DOW) confused? Typically the DOW will include crew and catering, whereas the BW will not.
Here's my take on the questions:
1) There are standard weights for crew (typically 85kgs for flight deck and 75kgs for the cabin crew on European routes) so the DOW will vary based upon the crew make up (i'm not refering to excessive lipstick). Crew weights will vary amongst airlines and routes, and some will have varying weights for male/female cabin crew.
2) BW does not include crew, whereas the DOW does.
3/4) As per Leezyjet