Your projections for the SPs are optimistic, as you've acknowledged, but not unrealistic. Taken individually, any of those guys could certainly reach those numbers. As a collective unit, it's unlikely IMO that they all perform to those projections.
That said, I think some might underestimate the effect Vazquez could have on our pitchers. It's possible that he could shave about .3 runs off of the staff ERA from the number of extra strike calls that he gets. And that doesn't include the "indirect" effects the pitchers will receive by being able to expand the strike zone.
A note about Masterson, which you alluded to with his FIP. He had the largest underperformance of SIERA last season, a difference of 2.03 from his ERA. That large of a difference cannot be sustained. If he's healthy, and with a good defense behind him, he should be much better this season.
Again, I don't expect the rotation to equal the Nats rotation. But they should be solid enough to give the team a chance to win most games.