No problem doing both if you are happy to give up some travelling time. New York is great but tiring and two weeks there can be tough. Give it three days, then go off to California for a week, coming back to NY for another few days. Flights to NY are plentiful and comparitively cheap. Don't discount Newark, nice airport and quite handy for NY. Internal flights in th US are good,cheap and easy. Watch the maximum luggage requirements though, they differ with each airline. I normally do a search on expedia.com to see who flies where and then go to the airline's own website to look for specials. Jet Blue, Spirit, Transair and other smaller airlines do great internet deals. The only other thing to do is to note the time diferences between the coasts. I would book everything here as you get better terms as a visitor that the Yanks do.