I'm going city hopping in a few weeks and need to buy some train tickets. I usually ask my hotel to book train tickets for me but I am not sure where I am staying yet.

Is it possible to buy a return Shanghai to Wuxi train ticket while in Chengdu besides going through the ticket brokers on the internet?

For the D express trains in soft sleeper, do these normally sell out? Could I just show up at Shanghai station and buy the tickets on the same day?

thanks