I know these snakes grow fairly large but so do them NZ White rabbits. But if you breed them you can cull them at any age to get the right size your snake can handle.
But even general crossbreds will work, too. They breed, and are hardy. Feed them a large variety of fresh foods, grass, hay and pellets and grain, and they should be quite a decent feed for your snake. Avoid giving them lucerne hay, it puts a lot of fat on them but the grass hays would be fine. They don't have to have hay if they have access to plenty of fresh grass, veges and their pellets. Check the labels on pellets at the produce and opt for one that is not more than 3% fat and about 16% protein.