1) some case need, some no need, for example: non-criminal record deed and working experience deed are need, born and (un)married is no need. but there has some way to avoid.
2) can't, should be signed by your recommender
3) can be different, otherwise, why they ask you 2 address?, don't know the rent info of mailbox in Chengdu, I don't live there.
4) must submit info from 18 years old wherever you lived.
5) not sure, seems can pass, don't worry
6)same as single, I think