Breeding Yorkies is probably not a lot more difficult than raising other breeds.  The MOST IMPORTANT PRINCIPLE is "you get back what you put in"  The most common issue is usually litter size  They usually only whelp between 1 and 3 pups therefore this is not usually a lucrative venture. My contact info is at 
MOOSEHEAD YORKIES if you would like to call me, I will give you the bestadvice I have.  Maggie