Yes, it is the correct procedure. SIA will provide you with a sample so the bank can issue the correct guarantee letter. 2 % is a little on the high side but since you're a new customer to the bank I guess you have to pay a bit extra.
They are not required for the interview. I know of guys that didn't provide them until halfway through their line training but that's not a good way to start your relation with an employer.
Good luck!