Why Hamilton re-uses actors between the first and second half

In the opening song, we hear these lyrics: http://imgur.com/a/ThVJV But we don't know who the characters are at this point, so we don't know whether Mulligan or Madison, Lafayette or Jefferson, Laurens or Philip, or Peggy or Maria is intended to be the one singing.

I think the point here is that it doesn't matter which character it is, since each pair plays a parallel role in Hamilton's life. Mulligan and Lafayette fought with Hamilton, alongside him in the war, while Jefferson and Madison fought with him, as political rivals. Laurens and Philip both died in his name. And the Schuyler sisters and Maria all loved him. So my interpretation is that Miranda re-used the actors in order to draw parallels between the various people who affected Hamilton's life.