How long does it take by bus from Nanning airport to railway station to Guilin?

From NN airport, which bus goes direct to railway station and how much? How many km is Nanning airport to railway station? What is the frequency and how long to arrive at the railway station? Do I need to book in advance for 'D' train (express) to Guilin? From Guilin railway station to town by bus, which bus plies the route? How far is the railway station in Guilin to town center. Thanks