As for what's off on the sketch itself, its the front leg. His body proportions are mostly right, its just the angle and width of the front leg that seems to throw the rest of it off. its a minor fix though. Here's where the error is:



The rest is well done though. As for measuring with heads for proportions, its a good base start, but fantasy art seldom follows. It's what gives it its characteristics. You see women with incredibly long thin legs to exaggerate curves etc Just as long as you don't go overboard, its okay to bend proportions just a little bit ^^

I hope Yoshida will see your drawing (well I hope he will see all of ours at one point). Great job and hope to see the colored version soon!