The problem with Jim Webb in the #2 spot is that he would be about as biddable as Bill Clinton. I like the guy a lot, but he's not one to subordinate his opinions for the greater good.
The guy was in the military. Subordination is the foundation of that experience. Also, he's still a politician. No one goes to Washington D.C., without thinking about whether he/she can eventually get to 1600 Pennsylvania.