Greetings,
Fuel has to be considered as payload, and to be added to the ZFW, the correct document is the AFM, where fuel restriction regarding using the Wing Fuel with fuel in the center tank, if there is a restriction then you are limited, due to wing to body attach. Sometimes scavenge pumps solve the problem and can transfer the remaining fuel to the wings, but only the AFM will give you the right course of action.
