It's not difficult to take the bus, since buses depart from Gongbei right at the border. Over the years, lots of foreigners have taken the bus without problem, since it was the main transport between Guangzhou and Zhuhai until the train opened.
Compared with taking a taxi anywhere, it's downright easy.
I've used the bus and metro. If the train stop (guangzhou south) is near the metro, IMHO, it's better for OP to use it. GZ metro is easy to navigate. While it's far, it's probably 40-50 mins to go to downtown. China bus station is a mess for non-mandarin speaking.