Embassy in london

Are you going to apply for the tourist visa? If yes, the duration of each stay is at least 30 days. For the exact days, it will be stated on your visa. If you want to stay longer after entering China, you can extend it at the local exit and entry administration before the expiration.

Yes, round-trip air tickets and hotel booking record are required for the application; or you can submit an invitation letter issued by a relevant entity or individual in China instead.