OMG, he looks so good even in this quick little sketch, I love it~!! Thank you!
Jack still looks humanoid in his non-human forms, he just looks more and more monstrous in a way that is still sort of beautiful. If I could draw myself, I'd love to show you a pic for reference, but...I've actually never been able to find a picture like how I imagine him to look, now that I think about it.
He's like right at 6 feet and he doesn't change size when he becomes inhuman. You could make his eyes a little smaller, if you like, but based off the sketch you gave, they look just fine to me. Also no, his hair doesn't need to be quite as long as in the reference pic.
Either or I can't wait! He looks so cool! And while the "frost" tattoo isn't quite what I imagined (more like vines of frost, instead of snowflakes) it still looks really cool and fits with the character either way! Oh, my heart can't take this! I'm so excited!