A:AnswerYou should have gotten a code printed on your receipt for that. Enter that code in itunes. Simply go to redeem code and you should get 4 free months. Make sure you turn off auto renewal though or you will get charged the monthly fee once your free months are up.
A:AnswerIf your AirPods have enough charge you can definitely use them while the case is charging. But you can only charge the AirPods through the case, even while the case is charging.
A:AnswerThey are headphones so yeah they are considered a good purchase. They can be use with any device that has Bluetooth included etc : iPad/ iPods/ other smartphone.