im 99% sure but i believe its 12 qts. maybe 13. and it should be Mercon V like you said. but someone might wanna double check my number ont he amount of ATF fluid.
If you drain every drain evey drop I believe Ford says it'll take around 16 quarts, including the tcase. But if you drop the pan and drain the tc then it should be right around 12-13 quarts.
And I'd use Merc/Dex III. That's what these transmissions were originally rated for and I've seen a couple guys grenade their e4od's from using Merc V.