Hi and welcome to YT. There are a lot of very knowledgeable people here that can give great advice.
My advice is to do your homework and really check out anyone that you are considering buying from. If you can find someone in your area that you can visit and see their dogs that is even better.
I bought my fur baby from a lady that I was able to visit her house for several times before I brought Onni home.
As for small, teacup is just a term and has nothing official attached to it. Many people use that term to charge huge amounts of money.
My Onni is tiny; 3lbs. She is in great health and has a wonderful little spoiled rotten personality. I think she just happens to be a runt and that is why she is so small. I will say this, being so small I worry wart about her much more than any of my other bigger dogs.
I believe the size issue is not as important as finding someone who breeds healthy happy dogs. There are many great breeders here on YT that can answer the more technical questions you might have.
I hope you find the perfect Yorkie fur baby!
__________________
Tracye - Onni's, Bonnie Blue, and Bella's MoM

Got Food? - http://www.gano.shelfreliance.com