One huge benefit from acquiring Choo: Arroyo wouldn't have to face him.
I'm not too bothered by the prospect of Choo in CF. 1. His steady stolen-base production suggests he has enough speed. 2. He has a tremendous arm. 3. He'll have good outfielders around him. 4. There's a relatively small CF at GABP. 5. Between platooning, Heisey, etc., his exposure in CF will be somewhat hedged. 6. He played a good bit of CF in the minors.
Also, I don't mind at all that Ludwick was signed first. It fills both the cleanup and leadoff roles, which is exactly what needed to be done.