You should really take the dog out for as much walking jogging excersize as you possibly can (got a treadmill?) so he can work off his energy & be more mellow. These are high energy dogs that need a lot of time if they have issues. You have to be the head muthafunster in charge & work to make sure he knows you are alpha dog. I'm sure you've seen Cesar Milan the DogWhisperer? He really has great techniques & reasoning on handling headstrong dogs. Check him out for help with your new dog.
We have had 3 Am.StafTerrier mixes, all were the most loyal, loving, clever & eager to please (once convinced you're the leader) dogs. Our current is what we & the vet think to be an american/english staff. terrier with some boxer in her. She is a love-thinks she's a lap dog, a very well behaved dog & is super super sensitive. If hubby & I, or even people on tv, laugh too loud, argue or get raucous, she gets nervous & clingy, then once assured all is well, she'll flop over onto her back & chill. she looks like she'd rip you into itty bitty pieces but she never has done anything negative or hostile to any man, woman, child, kitten, cat, puppy, dog, parakeets...she even plays gently with our bunny. It's really in how they're raised & making sure you keep any of their issues in check by daily excersize & training with lots of love, IMHO. Good luck in your endevour, I'm sure he'll be an awesome dog & a treasure to your heart.
a pic of her with our lil dog a mini-pin...crashin on the couch, as usual!