there is only one train from Guangzhou to Fuzhou, the code is 1234/1231, departing from Guangzhou East station at 09:10 and arriving at 05:33 in the next morning.
and yes, the train provides sleeper compartments. it costs RMB373 for soft sleeper lower berth and RMB240 for hard sleeper lower berth.
there are 12 stops on the way.