2 foreigners (visa Z and X) in china sending required documents for entry visit to hong kong by post

1- ID 1003A plus an attached photo
2- photocopies of passports and visa Z and visa X of residence
3- financial standing (bank statement and proof of employment) how much should have in my account? in my boyfriend account? can we send one bank statement for both of us? If so, how much at least?
4-proof of transportation arrangement. we are going by bus from guangzhou. how to get this proof, we don't know the day we'll travel exactly as it will be in 1 month.

A-Can we send our documents in one enveloppe?
B- Is there any other requiered document missing?
C-How to send the fees if any cash can be sent in the enveloppe? Is it by paying by ATM machine and sending the slip with the application form in the enveloppe? If so, what is the account number to send the money to? How much is he fee?

the stay is 7 days for marriage registration.

Thank you very much for your answer. Dali