Well, what a machine! I spent 7 years flying around Europe in it- it's the best handling machine I've flown so far.
To chuck in my two pence worth - our company used 100lbs per minute in the climb. In the cruise, assuming a max take-off weight of 116000lbs, fuel burn started at 5000lbs per hour decreasing by approx 200lbs per each flying hour thereafter with an endurance of up to 9 hours.
Max payload obviously depended on the dry operating weight of each airframe but max payload is generally considered to be 32000lbs (14.5 metric tons)
Regarding the 2 crew operation - Lockheed originally designed it to be operated by 2 crew, ie captain and first/second officer, but the unions in the USA at the time wouldn't allow it so Lockheed had to give the FEs a job hence a 3 crew op.
Airspray Canada were the first company to operate the Electra with 2 crew as the Canadian CAA were the first to approve it. Based on that, the UK CAA also allowed it to happen. The modification is simply to duplicate a couple of circuit breakers near the captain so that he can operate them in accordance with any abnormal check-list that requires it.
From my experience, having an FE in the middle seat can cause problems with CRM issues.