While consulting a veternarian is probably the wisest step to take, there is some general information that is available to you from different sources.  One of the basic considerations is the breed of your dog.  For, larger dogs generally tend to have large litters 8-12) even if they only mate once during their eleven-day fertility while small breeds have from 2-4.

Before you breed your dog, you may want to consult, not only with the vet, but with a breeder since there often is great expense involved as many things can go wrong.  If, for example, a dam has a "mummy puppy" which is one that has died in the womb and comes out looking mummified, the mother will likely suffer an infection of the uterus.  Caring for the babies and providing the required shots, etc., before their sale can also become expensive.

It is recommended that an owner not breed her female before she is two years old.  By this time, she has fully matured and pregnancy will not take too much away from her physically; also, she will be mature enough to handle motherhood.

Check out the site below and, please, do consult with professionals.

The number of puppies a dog can have in one litter does not really depend on how many times the dog mates.

As you know, each puppy comes from the union of one sperm and one egg.  But every time a female dog mates, it's going to have huge numbers of sperm ejaculated into it.  So it's not like having the dog mate more than once is all that likely to make it have more puppies.

However, it is possible that the more times she mates the more puppies she will have.  This is because sometimes the eggs are not all released at once.  So if she mates early in the cycle, all the eggs might not be present.  Some might get fertilized then and more could be fertilized by a later mating.

What actually determines the number of puppies a dog has is the number of eggs she releases.  Female dogs can release anywhere from one to a dozen eggs in any one cycle.  Once she's in heat, there's nothing that you can do to affect how many eggs she releases.