applying for a Chinese visa in seoul for a New Zealand passport holder

Hello
I am a New Zealand citizen and passport holder. I intend to travel from Korea to Beijing (ferry / rail - about mid June) and then make my way to Mongolia. After about 30 days there I intend to travel back to China and make my way south to Hong Kong. This means two entries into China ( about 10 days initially and 30 days for the second visit ). As I am unsure of exact dates I will be entering China I would like to get a double entry in Korea ( just before I go ). Is this possible or must I get it in my home country? As I do not know exact dates or where I will return to NZ from is it essential to have a return ticket, and accommodation booked?