Its really as simple as this: they didn't want to give away who rulk was so they had to lose the mustach. Now since everone is aware of who he is, i say thunderbolt should rock the stach in hulk form for sure.
The thor episode of Avengers: Earth's Mightiest Heroes had frost giants in it. I am assuming the cartoon is meant in some way, by marvel/disney, to prepare people for the Avenger movie. So yeah it looks like there will definitely be frost giants.
I have to agree with Aiden Cross, but i don't think its doubtful. To me it seems fairly obvious that it would be Amadeus Cho. Cho has shown Thor and others that he can be a hero by taking up Hercs mantle while he was away. I think it would make sense to use an existing character that some people are already invested in. Could be an interesting character if done right.