For the first few weeks best to use the same food the breeder was giving the pups. Then change to another food slowly once he is used to his new home. Changing home is extremely stressful, best to leave diet as it was or you can get into a horrible loop of nasty stool, accidents in the house and so on.
Yep, I'd stick with what the pup is already eating for about a month. Then if you want to switch, any meat based kibble that is small with around 30% protein should be fine. I find my small dogs don't do good with lower protein. A few decent brands that come to mind with small kibble are Ziwipeak, Earthborn Venture, Annamaet, and Farmina. All foods my Chi has done good on and I feel are good quality. There are plenty of others out there but those are what come to mind. Good luck with the new puppy. They are a ton fun!