Hi I am a US Citizien and my husband is US green card holder.

We'd like to visit Guangzhou (during the export import exhibition in October) and Macau, but our plane is landed in Hongkong. We will be travelling for less than 30 days.
1. As far as i know, we dont need any visa to stopover in Hongkong for couple days before entering to Guangzhou. Is this correct?
2. We do need tourist Visa to enter to Guangzhou eventhough our purpose is to visit the export import exhibition and sightseeing in Macau casino.
3. What is other requirements to bring with us when we apply the china visa in Los Angeles?
Thanks