From Pudong Airport to Nanjing Railway station

correct me if I'm wrong my friends, for what I collect from this site, I think I need to take bus shuttle Line 5 to Shanghai Railway Station then take train to Nanjing Railway station.
will there always be ticket seat available in bus and train? or should I book ahead?

I am from Indonesia and I will be bringing a 21" suitcase and a backpack with me. will the bus luggage capacity okay with it?

Thank you everyone. any response will be very appriciated