I've several iPhone/iPad, do I have to pay each time for in app purchases ?
No, you don't. ll our in-app purchases content are "non consumable", meaning that as soon as you paid for them, you can install them on 5 devices without paying more. For that, "buy" again the in app purchases inside the game, you won't be charged again if you do use the same iTunes account, with a limit of 5 different devices.