so, can we conclude the force vectors net zero at the center / 0V, acting on the molecules ?

when the +/- e fields overlap, if that is possible at all, won't that create a net 0 e field vector?

not exactly, there is voltage gradient across the gap, the direction is constant, but the magnitude just happens to switch from positive to negative

voltage means "difference of electrical potential"

so 20+ and 20- volts is the same as 40 volts, (the total difference of electrical potential is 40 volts) but since we "know" that the 20- volts is caused by extra electrons and the 20+ volts is caused by missing electrons then we can understand the distinction

and this is an important distinction because it relates directly to the force on the water molecule

20+ ----- 10+ ----- 0 ----- -10 ----- -20

40+ ----- 30+ ----- 20+ ----- 10+ ----- 0