Questions for Visa when traveling from Hong Kong as a tourist

Have emailed and called SF consulate but have not yet reached anyone there. Hope you can help.

I am an American citizen living in Seattle. In a month I will go to Hong Kong for 10 days to visit a friend there and to be a tourist. He suggests I visit Guangzhou for a couple of days while I'm in Hong Kong.

To go to China for just a few days, will I need a visa?
If not, what is the maximum time I can go to China from Hong Kong without a visa?

2.2 If I do need a visa, is the cost of visa different depending on what I put for answer of question 2.2? If so, what are the costs?

For 2.3, can I put approximate date? Or should I put earliest possible date, such as if I go to Hong Kong on May 24, the soonest I could go to Guangzhou would be May 25, so is that the date I should put on the application?

2.5 I do not know where I will stay in Guangzhou. Should I put my friend's Hong Kong address and phone number or should I leave blank or put the name of a hotel in Guangzhou where I might stay?

2.8 and 2.9 I do not have a contact in Guangzhou. I know no one there. Should I put my friend's Hong Kong address and phone number or should I leave blank or put the name of a hotel in Guangzhou where I might stay?

Sorry for all the questions but I want to be sure I need a visa and if I do, I want to give accurate answers. Thank you.