To answer question 3, you essentally set up the following equation using Q or K for the equilibrium where the concentrations are expressed in molar concentrations. That is:
delta G = Standard delta G + RT ln Q
where standard delta G is the standard free energy at 25 C, one atmosphere KJ/mol, all you have to do is first calculate Q which is calculated from the given concentrations in the problem which is as follows:
Q = [(2x10^-3)(2x10^-3)] / (3x10^-9) = 1333.33
So ln Q = 7.195
Finally, delta G = -42.3 KJ/mol + (8.3145x10^-3 KJ/mol K)(298.15 K)(7.195) = - 24.5 KJ/mol
This value indicates that the concentrations you gave implies that there is no equilibrium yet and the reaction will proceed until equilibrium conditions are achieved. In otherwords, if the concentrations you gave me were exactly the amounts required for an equilibrium condition, no reaction would occur and thus, delta G would then equal zero. So delta G is quite dependent upon Q or the actual starting concentrations you gave me. I am also assuming you wrote out the starting concentrations correctly as well.