Small puppies comes with small bladders - they need to potty every hour when they're around 12 weeks. By 5-6 months they need to potty every 3-4 hours. If you want your puppy potty trained, be prepared to put in the time commitment for this. If you end up getting a puppy under 4 lbs, be prepared that your puppy might have more difficulties getting potty trained (small dog = small bladder).
So, if you don't mind me asking, how many hours will you be working? I would say anything over 8 hours is too long. They need lots of your time or they'll become bored or depressed and that may lead to becoming destruction. I personally work 7-8 hours and I feel like I don't have enough time to spend with my Yorkies with the dog walks, training, playing etc on top of my own life. They're really like full-time life-long babies!
I should also mention that time commitment to training is just as important or you'll end up having a dog that will make you miserable because of behavioural issues.
Sure, newborns under 12 weeks may sleep a lot. But by the time they're a few months old (should be
minimum 12 weeks before any breeder should allow you to take the puppy home otherwise they don't get the chance for their birth mom to teach them the ways of puppy life), they're full balls of non-stop energy. You'll be happy if they nap for half-hour to one hour intervals!
With their energy level and potty needs, they definitely won't be sleeping 13-18 hours straight. Perhaps some other breeds sleep more. Yorkies generally have a LOT of energy. They
need your attention.
If you found a breeder who you think "cries puppy mill" but you still think it's worth the risk, that's kind of up to you. Some issues don't reveal themselves under after the puppy is 1 year old. I've read several stories about how ill-bred yorkies passing away due to health issues between 2-4 years old. They're
very very very devastating and sad stories! This is why most of us here emphasize finding a reputable and ethical breeder, otherwise, adopt. I would believe most breeders who are after making money don't really care about breeding pups with genetic diseases. That's the general consensus around here.
*sorry for all my forewarnings - I just want to make sure you're aware because there are just too many puppies that are abandoned by those (not saying you will) who were unaware or those who suffered losses due to lack of research of breeders. In either cases, the puppies are always the most innocent 