Probably been covered before, but do you need to move 10 ft. before attacking to gain the benefit of Skirmish, or can you attack, tumble and move 10 ft.?
You gain the benefit after you've gone at least 10' from your original position. In your scenario, you get the bonus AC after you've moved, but it's too late for the damage.
I believe that it says that you get the extra damage in any round that you move 10 feet or more under your own power. It doesn't say at what point in the round you have to move to get the skirmish bonus.