I really like this trade. This really improves the offense. Getting Choo puts someone at the top of the lineup who isn't allergic to 1b. The defense took hit, how much of a hit is a big question. If Choo can play a slightly below average CF then its a big win for the Reds.
The writing was on the wall for Stubbs. I think Walt knew he couldn't go into the 2013 season with him starting and leading off. As for Gregorious I don't mind losing him. He may end up being a better SS than Cozart but Zack isn't exactly a slouch. The Reds now have 5 years to find a suitable replacement for Cozart.
As for the question of who backs up Cozart, who cares? I guess the answer is who ever is playing SS in Louisville. I don't think you can go into a season worrying about who is the backup at every position. Gregorious value may have never been higher, no sense on holding onto him if he isn't going to see the field.
Now adding to my wish list, go sign Tony Plush. Heisey is going to see a ton of late inning action if he isn't starting. Heisey is an average CF defender, Plush is better. I would rather have him on the bench than Xavier Paul.