I know I am very late to your vote about keeping your acquisitions narrowed vs. much broader.
I had to do a quick query of the teams and cards available and I think you could play this for a long time and grow to a good Perfect league team with the given cards in the game.
It looks viable since there are some great High End cards or players that provide strong defense (Andruw Jones, Beltran, Ashburn, ...) plus plenty of players for the leagues along the way.
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