I am answering your questions one after another.
1. Make photocopy of your transcripts and certificates then submit that to controller sections of different universities, as you mentioned, attaching with Academic Records Request Form.
2. Controller section will verify and attest those docs giving seal and signature on Academic Records Request Form.
3. They will give you all the docs within a sealed envelop. Or if you pay them, they will send that with their own responsibility. But I will suggest you to send by yourself. (Caution: don't open the envelop).
4. It is better to send separately because in sender's address and telephone number section on envelop you have to write the information of controller. In place of sender's address don't write your address.
5. WES will accept only DD or CC payment. But DD will take long time for processing. Credit Card is the best way for payment and smooth processing. If you have any friend or relative CC holder in CA, it will take only few seconds for payment.
6. Yes, you can change the payment mode in WES website.
7. Anyway, have you got WES reference number? Are all the universities your obtained degree from Bangladesh?
Here before number 1, start #7, which is getting WES Ref no. that you will get it after paying WES and put WES Ref no. on "Academic Records Request Form" in the place where writing option is available.
If you do not put Ref no on "Academic Records Request Form" and get it sealed off by the uni/institution , well things will be delayed.