He could just be excited about eating so he does not take his time with it, instead he just scarfs it down so quick that he does not bother to chew. You can help prevent this by putting something like a small dish in his bowl so he has to push it around to eat his food. They sell bowls like this and if he continues to not pace himself I suggest looking in to buying one. But the problem should solve itself after a while.
Dogs do tend to vomit when they get over excited after eating or drinking, even if they eat or drink too fat this can cause them to throw up. Just make sure you get your dog all his shots so he does not end up getting sick, and take him to the vet for a check up to make sure everything's running properly. If it starts to be a real concern for you then you should not hesitate to take it to the Vet to get him checked out.
As for the humping, if hes not fixed then that could be why … just get him neutered and he 'll stop. Or may be your poor dog sounds like he has a bad or rotten tooth or infected gum as he wont chew food because its so painful to do so. a vet is expensive but so is him getting complications from him not following his food properly and you taking him to the vet to fix that up later on down the track