Payment integration: how do you implement PCI DSS? How to store payment token?

Let say our magento need to integrate with a payment gateway and we have mobile app(as FE) where Customer use to purchase product. We need to build credit card form and in the form we have a checkbox to “Save card” info for later use. I would like to ask your experience on how do you do this.

1. How do we implement PCI DSS compliance in this case with Magento? Just high level advise is very appreciated.
2. Save card: when we get payment token from gateway: how do you store it in db? Do you encrypt it? If yes, what is secure enough way to encrypt?

Thank you for reading and appreciated all your comment.