This is an awesome idea overall, but I think it goes without saying that you need to be very careful not to run afoul of an EULA. At what point does playing "with" the player become giving the player ingame items for real money? If you share quest rewards equally, you're probably OK, but what if the companion gives all of the gold rewards to the paying player? What if the companion runs them through a dungeon and gives them all the drops? At that point I think you're essentially selling the items for real money, which violates the EULAs. Tread carefully.