U.S. citizen applying for Chinese tourist visa from Vietnam...what should I do?

Hi, I am a little confused about the L type options. I want to get a tourist type for China (I'm US citizen applying for it from Vietnam). Which should I apply for- the single, double or multiple entry? I want to stay in China for the 2 (or 3) months maximum allowed, and then exit China for the day or days in Hong Kong and then come back to China for another maximum stay, and then repeat the process for a year. Should I and can I apply for the multiple entry type from here in Vietnam? Also, must I show confirmed hotel and round trip airfare to get the L type (even if the bookings places and times may change)?