I like the general idea, looks like it could run fast ideally.
I think you mis-counted on turn 4's damage though... 2 Swiftspears + Prowess from
Atarka's Command = 2 2/3's, plus the +1/+1 from
Atarka's Command make 2 3/4's = 8 dmg. Then there is the
Prophetic Flamespeaker with
Atarka's Command +1/+1, which is then a DOUBLE strike, so another 8 dmg.
Therefore, turn 4 you are dealing 16, and 3 to the face... technically.