You got good advice from your vet.
First of all, though, start with the NILIF "training". Buddy has to "work" before he gets his food. At first and for some time thereafter, the "work" can be quite simple such as a 'sit'. But later on, you may mix in some harder tasks such as 'watch me', 'curl', etc.
Second, pick one high-quality food and stick to it. There is no reason to keep changing foods and many good reasons not to. Follow the amounts for your size dog.
Third, offer the food for only a short time. Fifteen or twenty minutes is the general recommendation but since you are doing corrective training, you could start with a little longer period. Do not leave any food down after the time period expires - if the food or any part of it is not eaten, remove the food and the bowl and put the bowl away until the next meal.
Remember that very small dogs have to be fed small meals - so you will need to feed multiple times during the day. Some small dogs do get down to one or two meals a day but many of them stay with three meals. Simply divide the total daily recommended amount by the number of meals. Each meal is separate - do not carry over any leftover food from meal to meal.
