Cooper could sit by 10 weeks of age. It's best to start really early so if you decide to take him to an obedience class later, you've got a head start and it makes it easier to do the more "accelerated" stuff.
Old Mother Hubbard puts out a treat called "Bitz" that are small and work really well. You can find them at both Petsmart and Petco. That's what I used with Cooper so I didn't have to cut up big treats.