1 - 3 day visit to China

We are looking at a cruise leaving Shanghai for Japan and returning within 6 days, my question is.
1. We will be in China for between 1 and 3 days before the cruise, is the G type form (V.2013) the correct application?
2. One of the questions on that form asks, " Information of Inviter in China" How do I fill that in if i have no one inviting me as such to China? and,
3. Upon returning from the cruise, we again have 1 night in Shanghai before flying back to Australia, do we need the 2 entries type visit to re enter?

Thank you.