Won't work for credit/debit cards, can't extract the encryption keys needed to confirm transactions from the original card. You can try it without the ring, just use the flipper to try and emulate the bank card and use the flipper as if it was your card. Won't work.
To get a bank card ring you could open up the card, take the electronics inside, and diy a ring with it inside. I'm sure someone out there has done it
I dont have the game installed to test it but:
Look into the cs.rin forums for "Goldberg Socialclub Emu", I think Darck used goldberg's emu but it might have been updated since.
You can find the forum link in the megathread listed in the sidebar here. In the post there is a zip file with the goldberg gta4 files, you should be able to click and drag them to the same folder as the gta exe.
Hope this fixes it