Here is a very good website that talks about the different vaccinations and their recommendations:
K9 guidelines
I use a holistic vet and he recommends not starting vaccinations before 9 or 10 weeks. He actually prefers to wait until the pups are 12 weeks but everyones situation is different. You cannot follow the same vaccination protocol for a Yorkie puppy as you would for a large breed puppy that may be outside and at more risk of exposure to parvo. Also most large breed dogs are weaned at an earlier age and therefore they would need the vaccinations sooner. My puppies are usually not totally weaned until they are 8 or 9 weeks old so they are still getting immunizations from their mom. Giving a 6 week old puppy a shot could actually make them more vulnerable to getting parvo.
I do not start vaccinations on my pups until that are around 10 weeks old or older depending on their size. My advise is to do your research and do not over vaccinate. Mine just get distemper and parvo only. There is a wide range of opinions on this subject so you will ultimately have to make a decision that is right for your situation.