If you want him short, you'll want to use a blade.
7F will leave 1/4" of hair on the body.
4F 3/4"
30F w/1" comb will leave 1" of hair. You can also use a 10 or 40 under the comb.
I recommend getting this clipper set, it comes w/everything you need.
PetEdge: Andis Easy Clip Clipper Kit
The Fromm shears are great.