I would advice against giving soya. Chicken is meat and good source of protein. I would advice though giving organ meat in smaller quantities once or twice a week. Dogs are carnivores, cereals are not generally well digested by dogs, instead of wheat you could give rice as it is more palatable. Diversity in food is good you could try other foods like egg, fish etc as those contain valuable nutrition and your dog will love the variety. Also, you don't have to give him food 3 times a day instead 2 should be sufficient. In addition, few times a week a vitamin and mineral supplement should be quite sufficient. Remember, you don't have to give perfect proportions, balance is achieved over time.