Can I spend overnight in Chengdu Airport?

My arrival time to Chengdu airport is 02.00 am. and I want to go to the Chadanzi Bus station to buy ticket on the same day. My question is 1) Can I spend overnight in Chengdu Airport for about 3 hours? 2) Is it possible for me to buy ticket to Jiuzhaigou without advance booking. Which bus station Xinnanmen or Chadanzi has more chance to get the ticket? Thanks very much.