Actually the 600EX-RT can be used as a slave or a master. That means is that it can control or be controlled, so you might not ever need a ST-E3-RT & no you would NOT need any PocketWizards. Say you have two 600EX-RTs & one ST-E3-RT. With that setup if you need to use a speedlite on the camera you can use that flash plus control the other 600EX-RT that is placed somewhere off camera. You could also have both 600s off camera & control them with the ST-E3-RT, if you don't need a speedlite on the camera. Another VERY NICE feature is that the controls, buttons & menu on the ST-E3-RT is IDENTICAL to the 600EX-RT, so you only need to learn one menu system. If the speedlites give you enough power & recycle speed (which I assume in your case it will be plenty) then the 600s are the best, most controllable, easiest to use & most versatile system that you can buy into. Canon hit a homerun with this one!
P.S.- The ONLY way that Canon could have made this system better is if they would allow PocketWizard interconectability. That way you would be able to fire monolights or powerpacks from the same controller.