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The program is 100% able to be completed without buying anything.
12 points from moments
20 points from general missions
18 points from the bottom 3 tops now missions
The first 2 gets you 32 points to get the first 2 cards. Plus there are S2 tops now cards in the team affinity program packs. You never have to do the awards series missions to finish.
If I counted right 18. 2 missions at 1 2 and 3 each and 6 from making the playoffs missions
They haven't given a ton of detail about it but the season 1 cards are not completely unusable after season 3 starts. You still have them and can use them vs cpu and the wild card spot will let you use 1 card from an older set still.
I would not be surprised to see events that allow you to use cards from older sets later in the year. Something like set 1 and 2 pitchers against set 3 and 4 hitters for example. And I would expect after the postseason all cards will be usable but that is just a guess