That sculpt looks great! I think with the right colouring on it, it'd be awesome as is.
But I do have a question.. why not just use the head of the person inside the costume as the human's head? Might add to the creep factor that you can make gurgly sounds or something. It'd be simple enough to take what you just sculpted and cast that in latex to then apply to the costumer's face, blend it in with stage makeup, etc.. And you could build a little stirrup, if you will, to rest the head on so that you don't get a crick holding it there.
D: I dunno, just my two cents.
Like what I'm seeing so far, good luck!