I like your hitting you have good power and some decent speed you have a few guys that might kill your batting average but you have 4 or 5 guys that hit well for average that could make up for it.
I don't think Chris Snyder is the starting catcher for Arizona so it might be worth it to drop him for someone that starts if that's possible the rosters look like they are big so I probably doubt there's one available. I noticed 2 of the 3 prospects are catchers and could both play this year.
As for your pitching I like Grienke one of the best, I think Hamels befefits from being around Roy Halladay and turns his career around it could take a bit though but I am high on him this year but I'm not big on some of the back end of your rotation you have a lot of guys who are coming of an injury(Marcum, Young), guys that bad years last year(Harang, Oswalt), although I think Oswalt is a strong candidate to bounce back especially if he stays healthy.
I like Buchholz he has potiential to be a stud.
I like Slowey he's a decent pitcher and I will say if Marcum is able to stay healthy this year he could be a steal, he hasn't pitched though in a year and a half.
Ian Kennedy has a chance to do something in Arizona and Wade Davis looking him up intrigues me they both have upside.
If also possible I'd suggest considering getting a 3rd closer but I think you can easily trade for one or get one on waivers during the year you can always get saves on waivers during the season(I'd watch the Cleveland and Toronto closing situations)
So in all I like your hitting and your top 2 Pitchers but I think the rest of your rotation could use a little improvement.
Always check the waiver wire you can get a hot breakout player through the year that could benefit either your lineup or your pitching I was able to get Zobriest, Street, Romero all off waivers last year.