how much food?

Don't go by what so-and-so's dog eats to rate how much to feed your dog. Don't even go by the label on the bag and definitely don't go by the "he's always hungry" look. Go by your dog's body condition!!! From what you have said about your dog, you are feeding the correct amount for now. As he matures and gets into more intense training that will change. His body condition will tell you how much he needs to eat. Your dog, his pedigree, your training schedule, intensity of training, local weather, etc all play a role in dietary needs for your dog and these vary from person to person, from breed to breed and from region to region. It's much healthier for the dog if you err on the side of feeding him a little bit less than if you feed him too much because then you have an overweight dog that could develop into health issues down the road.

You have to think about the amount of calories, the bioavailability of protein, and the metabolizable energy in the food, not the amount of food itself. If your food is high in calories and ME and the protein has a high bioavailability then you shouldn't have to worry about the amount you are feeding. If you don't trust that your food has these qualities then might want to research some foods that do.