Is there any direct bus service from Baoan airport to Guangzhou directly? If yes, where to board at the airport? what's the bus or coach fare?

I'm afraid there is no such bus taking you to Guangzhou. If you wish to travel by bus, you can take subway Luobao Line at Airport East MTR Station to Zhuzilin Station and then walk to Futian Bus Station, where there are frequent buses to guangzhou. I remember the bus fare is CNY65/person.