Tickets from Guangzhou South Railway Station

I am planning to buy a high-speed train ticket from Guangzhou South Station. This is my first time in China, and I want to know the following: (a) Is it possible to buy a Guangzhou-Shanghai high-speed ride ticket directly from the South Station? (b) Will there be staff who can help me in English? (c) If I plan to buy the tickets 2-3 days in advance, is there any chance of the seat being fully booked and me not getting a ticket?
Will be very helpful if you can kindly respond to my above queries please