Wow. Thanks for all the feedback.
As to Kemmrich's Melodyne question, I just used Melodyne Editor 2, the AU plug-in, on a track I'd doubled, dragging the notes around until it sounded good. I also tried creating harmonies in Antares Harmony Engine and Harmony EFX, but the result in Melodyne sounded more natural (though it could be I'm just more familiar with Melodyne).