Best states to visit in USA for two 19 year olds? PLEASE HELP?!?

So im from Australia and my friend and i are planning a trip to the US for this time next year, around halloween. We want to go to Disneyland/world and universal studios and things, so we've kinda narrowed it down to Florida and California. I think id really like to go to california and go to hollywood and stuff. I also want to visit New York i think. We're also very interested in history and will probably go to museums and stuff, whats the biggest and best in america? plus im obsessed with animals, so id like to go to a good zoo while over there. any advice guys? also is this time next year a good time to travel? whens the cheapest time to travel around the us? thanks so much!