I've never bred any saltwater fish, but I do know it's not always easy for most people to keep the fish alive long enough for them to breed.
If you're starting out, I recommend starting when the Clowns are very young. That way they can go through their sex change period. Then you're guaranteed a male and a female. Females are larger than males. Feed a good and varied diet to make sure they're in good health.
Do also know saltwater fish live longer than freshwater fish. Some can live up to 10-20 years in captivity. So basically your main worry would be to get your fish to sexual maturity at around 3-5 years. Size does not dictate the actual age of Clowns (so I've read). According to the book, they have some weird phases they can go through in their life cycle.
There are more details that I don't know about. But I just wanted to pass along the main concern of just keeping your fish long enough for them to breed. Look to people who've actually bred Clowns though. for more info. It's actually not as straight forward as you might think it is.