Lands to add:
Myriad LandscapeReflecting PoolTransguild PromenadeRupture SpireAnd 3 or 4 basics.
Witchbane Orb is probably not good enough for its cost.
Crystal Shard isn't reliable enough I think.
Banishing Knack and
Retraction Helix could be
dead draws because you don't have a lot of creatures.
Sorin's Vengeance can be replaced with
Exsanguinate.
Uncle Istvan and
Lightning Reaver don't do enough for how much they cost.
Vampire Nighthawk would be a better option than Uncle but there is probably something better than that.
I also think you might want more draw. You won't be able to rely on your commander for casting everything so having cards in hand is great.
There's some starting points.