Being a Dog Groomer, I use Oster clippers. I love the 2 speed. I buy mine from the pet supplies stores, or TSC. You can buy your blades from TSC as well.
It depends on how short you want your dogs coat.
What I do is I use the #10 for the under belly area, inbetween the hind legs, the pee pee area and the butt. I also use the #10 blade to get the hair along the bridge of the nose, and the goopy hair at the corner of the eyes (the part that connects to the bridge of the nose). I use the #30 blade to get the hair in the pads, over the pads and just behind the pads of the feet.
But again, it depends on the breed, and the hair.
The only time I use a #10 blade on a dogs coat, would be Cocker Spaniels, Schnauzers, Poodle's.
Depending on the breed, and the length of coat you want, pends the # of the blade.
I wouldn't go into any cheap clippers - stick with Oster, you wont be sorry.