There is no difference in available features. However, the device and OS used may affect display resolution or the way in which notifications are presented.
App data is stored on our servers, including in-app currencies. To begin using the app on another device, simply install the app, log in, and select your character. Unlike many other apps, there is no need to obtain a code to transfer to another device.
Yes. In-app currencies are stored in your Square Enix account, and will be retained even if you change to another device or OS.