1 - Is a standard weight assumed for the crew or is the BOW adjusted for each flight based on the actual crew?
It's usually a standard weight.
2 - Does the BOW include flight attendants?
Depends on the airline
3 - Does the BOW exclude cargo equipment such as tie downs, pallets, etc.?
No. These will be included in the cargo weight. Only the permanent fixtures in the a/c will be included such as locks/stops etc.
4 - Where could I find the empty weight (i.e. BOW excluding crew, etc.) for a Douglas DC-8-62(F)?
No idea.
Think you might get more responses if you put it in another forum such as f/ops/crewing/dispatch, engineering or freight dogs. Not that many spotters would know this info.