Yeah, let him get the hissing out of his system. He'll get over it after a while if you handle in persistently. And the air biting is probably either more of that, or something to do with the way he was hunting in his tank? But if you're keeping him well-fed, and if you stick to gentle, consistent handling, that'll probably go away, too.

Just don't drop him! That'll set you back a year at least.

(I did that---dropped my enchi when she was a baby. She hissed every time I picked her up after that. Can't really blame her.)