hi Mehdi,
actually as sohrad said before the total sum to be paid is still 1040$ for the first part u should have paid 75+475=550$ with 50$ less than what u said; if u paid more a little it's ok, they will send u back a cheque with the extra
as for paying the remaining 490$ yeah me too i would not wait for them to ask for it....but i would wait to have a client id so it will b easier for them after to add it to the file; inside Canada u can also pay through bank as A+M suggested; outside Canada the only way is online by credit card; but it's very easy, u register with an email to CIC, u follow the payment steps, then u get the receipt in the email which u print fill in and send

as for the file, don't think too much now, step by step....maybe they will tell in the sponsor approval email; but if they said they will send the new files starting with beginning of March then it's like that

good luck!