Thank you for trying the game! For the difficulty do you recall what season you got to?
As for what is permanant/meta. Currently all content is unlocked but undiscovered. Undiscovered is just a way of letting you know which cards you've ever acquired or not .
Card packs come in two flavors. Recruitment packs go into your recruitment pool which you get access to during the night recruitment phase. Kinda like if you could add a new chip type to the market in quacks.
The show case packs bypass the recruitment pool and go straight into your main deck. But they are more expensive and offer less choices.