Yorkies are wonderful. One of my favorite breeds. Growing up we had a Yorkie, we had to put her to sleep a few years ago at 14 (liver cancer). My parents now have another one, she will be three years old this month.
One of my CE classes last week was about changing the work up you offer based on the breed and I have some web sites to help you figure out what tests and stuff you should have done for each breed. It will also help you ask breeder the right questions about your possible pup's parents (things to ask if they have had in their line.) Here is one web site
www.caninehealthinfo.org (I just double checked the site and Yorkies are not up there yet. They have too many potential problems and a consensus has not been made on what tests to recommend. Some of the common ones to ask about are luxating patellas, retnal degeneration, epilepsy, allergies, severe dental problems.)
You can also go to Petgen.com for more information.
Despite all the problems I just listed, like I said Yorkies are one of my favorite breeds. Most all of them have luxating patellas, and that sometimes needs surgical correction. My yorkie growing up had epilepsy, though she was never bad enough that we had to medicate her. Some of the dental problems can be helped if you start the pup out early getting its teeth brushed and things like that. Also make sure all its baby teeth have fallen out by 6 months old. Where I work we extract any still there at the spay/neuter at 6 months, but some vets prefer to do pediatric spay/neuters at 16 weeks old (can be easier on the pup, and they heal faster), but then they have to go back in later and extract the teeth.
If you have any questions let me know. Oh and y'all get annoyed when I go on like this about animal medical stuff let me know. I know my family gets tired of it sometimes.

I will stop if you want me too, I just get so excited about what I do.