Chihuahua breeders: how often will you breed a dog that requires a C section? how about one that doesn't?

Uh, one c-section is really enough. After that you shouldn't breed them again unless you just really enjoy being cruel to animals. Most don't make it through the second and that's why. Even on the ones that do not require c-section, you should only breed those chihuahuas about 2-3 times max. They are small dogs, have different body conditions.