from Beijing Capital Airport to Nanyuan Airport

my flight arrives at Beijing Capital Airport at 2.40am (I do not know which Terminal, please advise) and need to catch a flight to Xiangfan at Nanyuan Airport leaving at 6.40am. How do I get to Nanyuan Airport and is it sufficient time (4 hours interval)? Which travel way is easier, by bus or taxi and how much is the fee? Thank you.