How to configure GoCardless with Pro Sites?

I want to be able to offer a GoCardless direct debit option via the manual payments.

I have been notified by GoCardless support that I simply need to insert a simple HTML link to their hosted direct debit set up page on our account.

Let's say a direct debit has been set up successfully by the client. Do I then have to manually create/upgrade their site?

Furthermore, how do I offer multiple gateway options to the end client. Is that possible?