Is there a limitation on this aircraft for operating with center tank fuel? If there is a limitation, then it would behoove you to land prior to exceeding that limitaiton if possible. If there is not limitation you're in no jeopardy of busting ZFW limits.
ZFW means Zero fuel weight and you seem to be applying a fuel weight to the ZFW to get a revised ZFW.
EOW would include unusable fuel for predeparture calculations.
BD