I would use raw goats milk until 18 to 24 months. After this age, he won't need milk any more as a nutritive. From that time on, I usually use almond milk if I give them granola or something else that requires milk.

As far as making sure he is getting the right amount of vitamins and minerals in his diet, one of the best things you can do for him is to make fresh juices and green drinks. If you will juice fresh fruits and vegetables, he will get a lot of great nutrition in a concentrated form. You can also buy herbal supplements or other natural supplements which can be added to juice or other foods you are giving him already.