If you're wanting to get into breeding, especially with small breed dogs you really need to find a mentor. There are situations that can arise that no book can prepare you for, and having an experienced hand there can literally be life or death.
With toy and small breed dogs there are important factors to consider, like the size difference between the sire and dam. Breeding a female who is too small, or to a male that is too close in size to her can kill her. C-sections are much more common in small breed dogs than average sized dogs, they are very expensive and the survival rate for mother and the puppies isn't exactly 100%. Without knowing what the actual size your female puppy will be when she's full grown, you don't know if it would even be possible for her to carry a litter out of your male.
Dekka brought up a lot of good points. There are misconceptions out there that mixed breed dogs are healthier. In reality, a mixed breed dog has a chance of inheriting genetic disease from each parent. In all four breeds that would be involved in the breeding you are asking about luxating patella is not uncommon and needs to be x-rayed for. And that is only one disorder. Whether a dog is mixed or purebred, doing the screening is very important to make sure they are not crippling the next generation of dogs with genetic disease.
Lastly, when you are mixing breeds it really becomes a crapshoot as to what you are going to produce. Especially when it's a second generation cross. Their temperaments, energy levels, coats, size, etc is going to be all over the place. When you consider that some of the main reasons given by people dumping there dogs are "he sheds too much, he bites, he's too hyper," etc. you can see the importance of doing a breeding that will give you a predictable temperament and other specific traits that you want in your puppies, so that the people getting them will be getting something they know they can live with.
The suggestion to get involved with a responsible breeder as a mentor is great! I have seen it work very well, and made for some very successful Jr. handlers, trainers, etc. One girl I know is making big bucks now handling other people's dogs at shows, and she's only 16. She loves working with the animals, and getting involved with everything.