I can't quite remember how I did it last year, but the Apple Card is tied to my AppleID. I need to use my login credentials to check the balance. I think maybe when the email code comes, you have to use your AppleID to activate it, so maybe there's still a chance that the code can get intercepted before you have a chance to redeem.
Yes, but you would have to purchase it at an Apple Store or Apple.com
Last year, you were able to purchase more than one. We purchased eight $100 cards.
Unless they changed the rules, yes. See above answers.