A:AnswerOf course you must buy your in home wifi hardware. Then you must pay your carrier for the service. In most cases your carrier charges are not based on usage; some however are so check to be sure.
A:AnswerDepends what you use it for. 32 GB is plenty if you mostly stream music and video from the cloud and there is still plenty of room to download full length HD movies to watch when traveling or out of wireless range. If you have a huge music library and need to keep it on your iPad then I would recommend the 128 GB model.
A:AnswerSue,
If the old adage is correct a picture is worth 10,000 words well then a video should do it better. Here is a youtube I found that should help you.
https://www.youtube.com/watch?v=DLk8bhdlmEE