Welcome!
If you do a search on this forum, you will find lots of great info on potty training.
As for food, it's all a matter of choice and what works for you and your dog. Just be sure there is no by-products, corn or soy! Examples of good foods are Innova, Wellness, Merrick's, etc. In the "Health and Diet" section, you can find a list of five and six star rated foods. As well as this site...
Dog Food Analysis - Reviews of kibble