Welcome. It's wonderful that you are taking this little fella into your home and family. It does sound like he could be a Yorkie Poodle mix. Any long haired dog is going to need a lot of grooming. Get a good metal grooming comb and pin brush and groom him daily.
Do you know how old he is? Puppy mills usually feed their animals poor quality food that tends to speed up the rotting of their teeth. When you get him to a vet he should have them cleaned. I hope that he doesn't have to lose any as many puppy mill dogs do.
He is going to require time to adjust to his new surroundings. He has lived for a very long time in a small filthy cage so going out into the big bright would could be confusing to him at first. I think there is a thread here on YT about dealing with a puppy mill dog.
http://www.yorkietalk.com/forums/gen...nt-advice.html
Here it is!