This reminds me of a funny instance I had with MBs. The short answer is yes, the same MB works for your entire stay. However, in the early days of Magic Bands, I had a 3 way split stay so I got, yes, 3 Magic Bands. Then dummy me (I thought) I forgot to change MBs when I went from stay #1 to check in to stay #2. "No problem" the front desk CM said, she took my MB, did some Mickey head to Mickey head magic, made the green light spin around, waited for me to go "Ooooh!", then handed it to me "All set!" So I didn't have to use MB #2. When I switched to stay #3, I just tried out the first MB and it worked, even without magic stuff at the front desk. So I came home with 2, brand new, never used, Magic Bands.
Sorry, I don't know about the credit card, though. Always pay the old-fashioned way-cash!