if the drive is connected to a battery pack or AC charger then you can still stream from it while it is charging. If it is connected to something that creates an MSC connection, like a computer, it cannot be used wirelessly at the same time.
iOS has an “open in” option. you can choose that when browsing files in the wireless stick. iOS will then look at the available apps on your device and display a list of app it thinks can use that file type. you can then open the file in one of the listed apps. doing this sometimes requires the file to be saved to the iOS device. Depending on the app and what files are being used.
