One or the other. IMHO, better to use stamps since it makes it easier on the person (or probably more accurately, the person's assistant) - they can pop the envelope into the mail rather than have to exchange IRCs for stamps.

Since you're sending to an address in Australia, your SASE should have Australian stamps. Whether you use IRCs or stamps, you should have enough of either to cover the return of what you're sending to get signed. An index card would probably use one IRC or airmail stamp; a photo, more than one, and your Post Office should be able to tell you the weight so you can figure out just how many.

I wish to submit an autograph request to actress Ms Naomi Watts.

Fanmail.biz has provided the address of Linsten Morris Management, which is based in Australia. It has also instructed me to buy *several International Reply Coupons, since I am mailing out from Singapore.

Given that the agency is in Australia and Ms Watts is currently residing in New York City, (1) How many International Reply Coupons do I need to purchase, (2) Will I need to stamp the Self-Addressed Stamped Envelope (i.e. the envelope that I expect to contain the signed photograph to be returned to my home address in Singapore)?

(3) If I have to stamp the Self-Addressed Envelope, what stamps should I use?

*I am assuming that my self-addressed envelope should take this path (Singapore -> Australia -> USA -> Singapore). Please correct me if I am wrong.