At 9 weeks he shouldn't need wet food added unless you wish to.
I always start with the bag recommendation and then look at the dog and adjust as needed. So if I knew there was a lot of exercise being done that day I would add a little extra, same as if I knew it would be a quiet day I would cut back a little. If I noticed the puppy getting chunky I would cut back a little, if I saw the ribs or backbone too much I would add a little
Go with the dog's current condition and you shouldn't have a issue