I and 3 business colleagues are planning to travel from Shanghai to Beijing the morning of June 8th.

We wish to travel business class. I have the following questions:
1. What is the luggage allowance? Will will all have large suitcases and need to make sure that we can take them on the train with us
2. How can we make sure that we are sat next to each other in the same train carriage? When you buy a ticket is a seat number assigned or can you sit anywhere in business class?

Regards
Charlie