For the luggage storage you can't use your credit card.
For he Maglev I am not sure, but I would not expect them to accept credit cards.

If you leave from T2, I suggest you storage your luggage there. It's about 15 minutes walking between T1 and T2, which can cause some stress if you have to walk an unknown route when you have to check in.

Cost for storage should not be more than 50RMB, maglev return ticket 80RMB (clearly ask for 2-way ticket, they usually will tell you it's valid only 7 days. Just acknowledge)

At Longyan road station you can go downstairs and get a quick, cheap meal at Ajisen Ramen or a real coffee and tasty cake at 85°.
Otherwise nothing to do at this station