How long can I stay in China with a 1year multi entry visa before I must exit to reenter? 2 months?

I want to live as a tourist in China for a year and will apply for a 1 year multiple entry visa. My understanding is that I will need to exit the country ever so often and re-enter during that year. When I apply will I need to show proof of a ticket leaving China? And how long can I stay in China before I need to leave and reenter during that year? Every 2 months? Would really appreciate some help with this!