[Ellie May]

You can mix them but don't have to.
You can give it once a week or once a day or three times a day.
Whatever works for you.
I am really picky, so I would probably find out the calories per cup in the dry and wet and find out how many calories he should have a day and give him about that amount total in wet and dry food (unless I was only giving a very small amount, then I would just give it and not worry).
That's a lot of work though, so most people just estimate.