Queries on buses and trains:

1. We are currently in Hong Kong, Imperial Hotel on Nathan Road. What bus should we catch to go to the airport and do buses accept octopus cards as well?
2. We are due to travel to Shanghai from Beijing on Sep 13th, to which station should we head to to purchase train tickets?
3. Same question to travel from Shanghai to Guangzhou?

Thanks already for your answers and thanks for the help. It has been very helpful for our trip so far.
Thanks so much.