Details needed for double and multiple entry visa

Hello,
I am going on exchange to Taiwan this spring. During that semester I am planning to go to the North Korea marathon and visit China before and after.
As the times for the marathon is not clear yet and it is not possible to apply for the visa in Taiwan I need to apply for double entry tourist visa from my home country with reebookable flights. I might also want to visit China more times while I'm on exchange, so I am considering a multi-entry visa as well. But when I type in the application form for the visa, I can only type the details for one entry into China. Will they ask for my bookings on the second entry? And if I want a multiple entry visa do I need to have at least three bookings? Also, how can I make sure the visa is valid for 6 months? As the marathon starts over three months after I leave my home country.

Best regards