Posey retired at 34. That seems about the oldest you could play a guy at catcher regularly. Even in that last year, Posey was playing a lot of first base. It's a demanding position.
I'll go out on a limb and guess that Austin Hays has a good chance to bat in the lead off spot. He's good vs LHP and he was batting in the #1 spot vs LHP last season.
I just dug into some statistics vs LHP and I was surprised to discover that Westburg struggles vs lefties. He's better vs Right Handers than left handers.
Cowser also had difficulties against lefties in his AAA Career.
I don't think Santander is DH because he's going to be in Right Field.