I did not inform QNC that I'm taking CAS. Their letter tells us that we have two years to complete CAS or they will close our application for registration. I don't think it would be necessary to inform QNC as it will be CAS who will inform them when we are eligible to register or not.
Yes I did use credit card and sent the details through email. The info was split into two messages so no single email will contain all details. I also used my credit card with a small credit line just in case.