Hong Kong tourist visa. Hi, I am Pabel from Bangladesh

i am an international student .I am studying at Beijing language and culture university. I have a questions.please make it clear.
1. Do you I need to purchase the tickets or reservation is ok? Because they said it's gonna take 4 to 6 weeks to know the result. If I book the ticket in advance the reservation will be cancel after 7 days.in that case what should i do .
2. Can you suggest me how much money much do I need to show in my account.