From Yiwu to Shanghai by road, you can take long distance bus at Yiwu Binwang Bus Station, takes around 5 hours to Shanghai.
From Yiwu to Guangzhou, taking bus is more expensive than taking train, train trip would take around 20 hours on the way.

Hi

yiwu-shanghai you can take fast D train it just take 2.5 hours, cost is around 100rmb, bus is a little bit dirty(bus is almost the same charge). Yiwu -Guangzhou bus is one og the option. YOu can take train as well. sleeping seat is around 350rmb, normal hard seat is around 170rmb. and takes17 hours.