Using Apple Wallet

Hi all,
My apologies if these are stupid questions or if the answer has been posted somewhere on this site and I just can't find it.
Firstly, I added two cards to Wallet, I can pay if I unlock my phone completely then go to apple wallet and double tap on the card.
I know you can open the wallet on your default card, supposedly by double clicking the home button, This is alicated to app swicher because of VO and I honestly don't think you can change that? If i'm wronge someone please tell me.
So how does that work exactly. Also do you have to double tap the card, or just set it as default and then change it to your other one if needed?
Related to that, I'm guessing when I get my 16E I will double tap the Wake button instead, making this post redundant?
Thank you in advance.
Regards,
Melissa.
PS:
When will they make it so you can do things with multiple presses and press and holds of the action button and the wake button? (LOL)
PPS:
What's the difference between the back tap that's in VO's settings and the one found in the touch settings, and can they be use to trigger shortcuts like to turn on and off VO on my (Haven't got yet) 16E?