Luggage allowance on High Speed Train

Hi

We have booked tickets from Shenzhen North to Guilin North station for 6 November 2015 at 11.48am. We intend to travel with two international hard suitcases size 28 x 22 x9inches and would like to know if we would have any problem taking these on the train and also the MTR from Kowloon to Shenzhen. We need to know this is ok so that any problems can be sorted out before we arrive. We are led to believe there is limited storage space on the high speed train. We understand that porters can help to carry the suitcases to the high speed train before other passengers board.

Where is the ticket office sited in Shenzhen North station and can we arrange porters easily for our departure time if we arrive 2 hrs before departure time.

We intend to travel back from Guilin North to Shenzhen North around 24 November 2015 (still to be confirmed) to connect with our flight out of Hong Kong. How soon should we book the tickets for this journey? Can we leave booking till near our departure or will there not be availability?