Yay!
If you decide to start the war, get those catapults out to the field of battle before going after Hammurabi. And remember that our military is mostly stationed near Peragus. Also, there's one axeman up north with a couple of extra exp. points, that might come in handy.
I'm thinking you should take out the capital first, to cripple their unit production capability, but that city with the flood plains might also be a good first target. The bugger will start whipping like crazy, as soon as you attack, so those two cities should be taken out as quickly as possible. Don't forget to raze the two cities closer to our empire.
Of course, if you feel you shouldn't attack during your 20 turns, don't.