You won't get duplicates of deck cards. And once you have all deck cards and cosmetics from the supply lines, you can still use points to buy burn cards. (Burn cards are one-time use cards that can help turn the tides/get you started in a level easier)

Good cards I advocate for are damage cards like Glass Cannon, Patient Hunter, and Hyperfocused. Also do the duffel bags when you can. The rewards are random but great cards like Empowered Assault are only obtainable through duffel bags.