I would say that for a 2-3 week trip you are not planning too much. They are all great locations with lots to see but with an average of 4-5 days in each location I think that should be enough time to see the sights. Xian is definately a good stop, with lots of historical sights to see.

Traveling near the first week of Oct. you should expect a greatly increased volume of toursists at the tourist sights, airports, train stations, busses, etc. It would be wise to have your hotels and flights booked in advance instead of waiting to book on arrival, which at other times of the year is normally fine and cheaper to wait. It is one of the major "golden" travel weeks here in China. Someone had the bright idea that it would be better to give everyone their vacation time all at once so that you can have the whole 1 billion+ population all on the move at once. What a bright idea that was. As long as you are aware and prepared you should be fine. The Oct. week is not quite as crazy as Chinese New Year.