The breeder and her health guarentee sound great! If I had 5,000 to spend and I felt really good about the breeder I would do it
I would worry about the size of the yorkie though. If you are set on getting a smaller yorkie perhaps you should consider the 3lb?
When I brought Missy and Max home they were both 2lbs each, my kids were very carefull with them but accidents do happen, Missy got hurt twice in her 1st month of being with us, she was so small and so fragile, I turned into the yorkie police and that was no fun for the kids either. Now Missy is 5lbs and Max is 4lbs and I am so glad they are at a size they are not as fragile. I used to think a tiney yorkie would be just fine in my home with my kids age 11 and 8 but after going through a few months with 2 lbs yorkies its sooo nice to have them a litter larger. I think 4lbs and up would be perfect size for a home with kids, thats just my personal preference. 4-7lbs is still pretty small