Pugs are hard to breed, as the breeder you spoke to told you regarding the small female. Those wide, flat heads and narrow pelvises do not make for easy whelping. Pug females can and do die, and an inexperienced breeder is far more likely to lose a bitch in whelp because they don't know when she's in trouble and needs the vet's assistance. Many Pug litters are born by c-section. Then there's the problem of placing the puppies.
People buy dogs for the oddest reasons.
Yes, you and I love our Pugs very much, but unless you are experienced screening buyers you might well end up selling to a lot of people who are not good owners, by any standards. When you breed, you have responsibility for the lives you produce. If you don't keep close track of your puppies as they grow up, you won't know if your dogs are producing genetic problems , so you could continue breeding dogs who bring nothing but heartache and disaster. If you don't take back any puppy, or adult dog, at aby time in its life, you will be contributing to the Pug rescue problem. All of this doesn't mean you shouldn't breed Pugs.