A:AnswerThat makes no sense because a lightning connection is the same across device versions. Are you sure your device is a real Apple product and not a knock-off?
A:AnswerI'm hoping you already found your answer but if its an old ipad then 128 or 256 would be plenty however you do not have to transfer in one go you can get the smallest available and transfer multiple "batches" until you have them all. if you really mean "very very old" just make sure it has the small "lightning connector" and not the wide "30 pin" connector that they started out with