Detailed itinerary, want to travel after study in China

I am from Australia and applying for the X2 Visa for 1 semester (3 months), however I plan to travel around PRC for 20 days after I am finished.
Should I choose the two entry valid between 3 and 6 months option, or select "other" and write 5 months?
Also, I have no detailed itinerary as it is 5 months from now, so how can I provide dates and addresses of where I will stay?
Thank you.