You really need 3 Winged Slivers.  They are essential to the deck's anti aggro strategy of building up a defense and then attacking for the win.   In aggro and aggro-control matchups drawing into one is often what wins you the game.  2 in the deck is just not enough.

You should definately go with 4 Cabal Therapy.  You have a ton of creatures which become weak after they come into play (Squire, multiple Ravenous Rats).  Also I would think that Faceless Butcher would go well in here. You could freeze cards in their hand over and over every turn until you therapy it away.

Have you considered playing Dark Confidant? He would be is an absolute bomb with the Sage bouncing into play over and over.  This deck needs infinately more Force of Will.    Finally, why only 3 Harpies?  I thought that was the name of the game.