First Basenji's

Yesterday was my puppy's first visit to the vet (with us). He is our first Basenji as well as our first experience with this Vet. Upon acquiring my basenji, I signed a contract with my breeder that stated he had to be neutered between 9-12 months. I told this to my vet and she said she disagreed with that and believed he should be neutered by six months because he could start marking and sometimes that that was irreversible. She also suggested to feed him a different food. My breeder recommended Taste of the Wild which is a more natural grain free food. The vet suggested a puppy food like science diet or Iams. I am not sure what to do or who to believe. I do not think my vet was familiar with Basenjis. She said this was the first one she had at her practice. Im not really sure what to do, any suggestions?