I don't know how much help I can be, but I'll try.
Diet: Check out
Yorkie Health & Diet - YorkieTalk.com Forums - Yorkshire Terrier Community for quality dog foods. Read the sticky about
Dog Food (Kibble) Grading Chart. Get him on a good diet. I'm having good luck with Wellness brand for puppies. Have tried a couple of the others, but they didn't agree with her. Coby is young enough he may need kibble to be soaked. Forget buying brands just because they are on sale. He needs a quality diet. If it's on sale all the better. Buy small bags as possible so you can see how well he tolerates the brand & whether he likes it or not. Do a gradual switch on the brands by mixing both kinds & gradually increasing the new brand over a weeks time. Doing this will help prevent tummy upsets that can happen if you make a sudden food change.
Housetraining: He's very young & it's going to take time & plenty of patience. When he's completed all his shots & it's safe to take him around other dogs, it's a terrific time to let the dogs teach him. Arrange some playdates with friends/family dogs if you can, or a park where dogs have been & he can smell it, or daycare. Roxy didn't learn to poop outside for quite a long time. It took two times at daycare but she figured it out. The other dogs taught her. There were good days & bad days during the whole process, so be patient. Take some of his poop outside & leave it where you want him to go. When he goes out, take him to that spot & let him sniff around. Just watch to make sure he doesn't eat it.
Crying: He misses his mommy & littermates & a little young to be separated from them. Many people aren't aware of that when they buy these little guys. You'll need to be
very patient. Roxy was already crate trained when I got her so it was not something I had to deal with. Hopefully some others here will be able to help you with this one.
Good luck!