Duration of each stay is granted on a case by case basis at the discretion of consular officers in accordance with relevant guidelines, if you can provide documents to prove that you need to stay in China for 6 months, it is possible for you to get a single-entry tourist visa with 6 months stay duration, however, generally speaking, the single-entry tourist visa has only 30 days stay duration. It is hard for you to get it if you just want to stay there for 6 months but you can't provide sufficient documents. The return flight tickets are required for China visa application, you need to pay for a Return Ticket to China.