Does the use of fling activate the pickpocket/magician ability making you grab their item after using fling to get rid of your own so that you pretty much have an extra use of fling?
No.
Pickpocket only works with contact moves. (Fling doesn't make contact)
And Fling doesn't activate with Magician, as per Magician's Bulbapedia page (https://m.bulbapedia.bulbagarden.net/wiki/Magician_(Ability))
