All my birds get Peach Face Mix which is nearly the same if not the same as Cockatiel Mix. That is from the Budgies right up to the Sulphur Crested Cockatoos. And that includes my pair of Suns and a GCC. The mix I use only has 10% Sunflower and Safflower. I presume NZ would be the same or pretty similar to OZ. Pellets are not a big thing in OZ and I would say NZ would be the same as us in that way. Pellets are ok if you only have a few birds but I have aviaries full and they are very expensive over here and seed is reasonably cheap and very fresh. Along with fresh fruit and veges and don't forget they also need some animal protein. This can be given in various forms like Egg and Biscuit (preferably home made) as the packaged mixes are very variable as to their contents some having little or no biscuit or whole egg but mainly bread crumbs and Custard Powder. In the wild most if not all birds including budgies will eat animal protein ranging from road kill to bugs and beetles. Black Toos and Gang Gangs love meal worms, especially young ones. I know it sounds gross but wild budgies have been seen at an animal body eating it.
They need BOTH seeds and pellets, not just one, an all pellet diet is just as bad as an all seed diet. My Cinnamon Green Cheek Conure gets Cockatiel and Budgie seed with a Gourmet Parrot Blend mixed in. She also gets a dish of pellets and eats both the seed and pellets without any problems.
Tiel sized seed should be just fine :thumbsup: what is the breeder currently feeding him? I would follow the breeders exact schedule and exact mix for the first month since you'll be getting your baby newly weaned and then change his diet from there to what you would like. If you have a specific food line you want to use, talk to your breeder and see if they can wean him onto it for you! The sooner he starts on what you'd like him to eat the better!
I second the sprouting suggestion. I do feed pellets as a part of my own bird's diets, but I live where pellets are readily available, and my birds were actually weaned onto pellets. Nevertheless, birds are certainly able to thrive without processed foods. Germinated seeds and nuts, on the other hand, would be a component of a wild bird's diet. This is why I suggest sprouts. They are just so good for them - and eat some yourself while you are sprouting.