Arriving Beijing on Dec 1st at 16:00 on Sunday

Would like to go to Keyilu subway station and then walk to my wife's appartment. From my research I have found taking the shuttle bus line 7 to West railway station and then subway line 9 to Keyilu.Would it be easy to transfer from the bus to the subway station and how do I do it? Where do i buy ticket for the subway? How long is the shuttle from the airport to the West railway station?
Thank you.