First of all, Welcome To YorkieTalk! I will offer my $.02, but am interested to see what others will have to say. In my own opinion, I think that he'll be just fine. She has obviously had satisfied customers in the past, and their dogs turned out okay. 7 weeks is about the time weaning comes around -- we let our mamma dogs decide when they should wean, we don't rush, but usually, they're tired of them at about 7-7.5 weeks. Before she weaned them, she should have been putting puppy food in there with them so they could start trying both so that they will be properly adjusted to going from milk to hard food. As long as the puppy has food and water, they would be fine overnight in their crate.
Also, in my opinion, crate training should start as early as possible. This helps the new owner finish the process. As far as bad habits and such things as that ... they're still puppies, if you are getting him at 10 weeks, you still have a whole heck of a lot of time to instill good manners and habits in him. (Though I would like to inject here that I don't like to see puppies leave the breeder until 12 weeks of age. There is so much that can develop and happen within a two week time period) At 10 weeks, he is obviously isn't going to be fully crate trained and is going to be a poopy little puppy like all the rest of them!
Good luck with him and I hope to see pictures soon!!