Hello and Welcome to YT. "Yorkies For Dummies" is the first one I recommend."Yorkshire Terriers: A Smart Owners Guide" is the second book. These are excellent resource books .Another book "How to Housebreak Your Dog in 7 Days" Is very helpful. They are not as easy to housebreak.
I would wait a month or two before changing over. You do not want to change everything to early. He left his mom and siblings. He has a new family. That is a lot for a little pup to deal with. You can do a search on our site, on the bottom of the page, for dog food. Everyone has different favorites. You can get idea of what is being fed. I feed Galen around 25% protein.
Also check out
Dog Food Reviews and Ratings | Dog Food Advisor . There is a ratings and reviews of foods. It is a great dog food site.
Good luck