first of all welcome to yorkietalk! There are many knowledgeable and reputable breeders on this forum who have really helped me and others immensely with their advice. Maybe you should post this question about what age the puppy should leave its mother on the breeders section of this site. I've always heard that yorkies shouldn't leave they're moms and litter mates before 12 weeks not just because of health reasons but also because of appropriate behavior the puppy learns from its mom and siblings. I'm sure some of our breeding experts can elaborate more.
As for estimating adult weight a rough guess is to triple the weight at 8 weeks or double the weight at 12 weeks.
As for advice, I agree with Amber, maybe the breeder can give you a blanket or towel that the mom has slept with to help ease transition. We put a teddy bear and little clock and hot water bottle in Bentley's crate for the first week or so to help ease his anxiety. Just be prepared to give lots of love and allow for plenty time for the puppy to rest in between play time during the day. Also keep Nutristat or Nutrical on hand for hypoglycemia.
Good Luck!
