I am no breeder or a pro on this subject but since you asked for our insight I can atleast tell you what I have learned.
I too months ago atleast thought about breeding Schatzie. I sat down and wrote out the pro's and con's of doing so then I got with my breeder friend who gave me more insight then I could have ever dreamed of. After doing all this I found out it was just way to many odds of things that could go wrong with Schatzie that I personally chose not to. The con's definatley outweighed the pro's.
Plus now with her situation of Perthes Disease in her hip she is in no way able to breed as it is hereditary.
I hope you research long and hard and find the info you need that will help you make up your mind on whether to breed or not.
I have heard and read that the male should be a lot smaller than the female however, but again I am not a vet.
The list of bad situations that could arrise from breeding for a hobby or just to get cute pups is so very very long and I personally was just wanting to take the risk of putting Schatzie in harms way.
Best of luck with your research, I am sure other Yorkietalk member's will give you plenty of known web site's to research and info too.
I wish I would have saved the list on con's that my breeder gave me as she is very much familiar with all this, however I did not keep it. I would forward it to you had I saved it. Darn it!!
Good luck!