Can we go direct from mongkok to Guangzhou by train and if so how long and how much?

There is no train from Mong Kok to Guangzhou. You should take metro back to Hung Hom and then take a train to Guangzhou.

In Guangzhou, there are many shopping centers, such as Shangxiajiu and Beijing Road. A number of wholesale markets of clothes and shoes is also a must in Guangzhou. These famous ones could be found around Guangzhou Railway Station. On the other hand, the train from HK will arrive at Guangzhou East Railway Station, walk down from where you could go to the prosperous Tianhe area.