Creating Big letter from many small ones?

Hello, I posted this on animation thread, but looks like this is more particles question.
I want to make a small animation in which I would make a big letter(and I mean A,B,C,a,b,c letters and such, not mail) gradually appear in high speed in 2-3 seconds, and lots of small letters would pour at high speed from the side of the scene and actually create that big one. Can anyone help me with some guidance about that?

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