When Rory was a pup, he got 1cup a day split into 2 meals. Now he gets 1/2 cup a day divided into 2 meals + wet food. Each dog is individual and you must feed them so they're not starving, but not fat either.
i'd recommend not free feeding. Cavs are very prone to getting overweight and this can compound their heart problems. (all that extra weight puts additional stress on their hearts and bodies)
I think a puppy should get more food as they are growing and need that extra energy.
Also - wet food is less energy dense than dry food. so you have to feed more if you're giving him ID or boiled chicken and rice. We switched the dogs to a hhome cooked food and Rory lost too much weight because I wasn't feeding him enough. He needed more of the wet food to get the same energy because of all the water weight in the wet food.
Dogs are not our whole life, but they make our lives whole.