What is the bus number to go from Macau to Guangzhou, from where to catch the bus in Macao?

There is no exact number. You are suggested to go to Border Gate and cross the border to enter Zhuhai Gongbei first. Then walk to Gongbei Bus Station to take a coach to Guangzhou in 2-3h. Or you may consider taking a high speed train at Zhuhai Railway Station which is also within walking distance to Gongbei border and it only takes an hour.