If you are combining physical cards, keep the card that you have loaded all the money on in your wallet. I have been asked to show the physical card when returning an item. You do not have to buy any additional cards. Once you have loaded them all in the site, just pick one, and transfer all the others to it. They make the process very easy. If they are all e-cards, perhaps take a screen shot after you are done consolidating the cards, in case you can’t access the site for any reason.
I have had one physical card I have been using for years, as the number printed on the card is larger and easier for me to read when I do Mobile Orders. I have moved money from both physical cards and e-cards to that card over the years and it was very easy. One time I had 20 $25 cards to consolidate, and it was very simple.