May I suggest starting with a good representative of the breed, first. Own the dog. Learn about the breed. Learn about health testing, genetics, drive, titles, etc. Put some titles on a dog. Learn what you want in a dog. Why do you want strength and stamina? For a running partner? For weight pull? For other Dogsports?
Why breed a litter of "pits?" It really sucks. You might get 8-10 pups. You'll keep one or two.. So that's 6-8 pups of non health tested, non titled puppies. Puppies who will range the spectrum in size, type, and temperament. You won't have a predictable "look." Plus, it's pretty freaking hard to find them GOOD homes. Homes that will keep the puppy until death do them part. That will take good care of the puppy. You sell these pups for $100 each, and you may sell them all, and not have to take them to the shelter, but at what price? And at $100 each, with all the vet care and extra food and supplies, you won't even break even. Not to mention all the cleaning and scrubbing, noise, and effort you will spend getting the pups to the legal age of 8 weeks, before you can sell them.
I just bred a litter that was from health tested and titled parents. Not including the amount of time and money it took to get the titles, I am in the hole, even with fetching decent prices for the pups.
The market is FLOODED with hum-drum, run of the mill, backyard bred pits. There is no reason to add to it.
Just sayin'.