Hey all! New on this forum and in desperate need of advice. I found a puppy on the side of the road about a week ago.. abandoned, filthy, starving. Rushed him to the vet and they gave him fluids and i had to bottle feed him for about a week. they estimated him to be only about 3 and a half weeks old. they think he is definitely a pitbull. (pic below, what do you think?) I have obviously fallen in love with him, but i've had a lot of confusion on how to properly discipline him. i do
not want him to be scared of me, i just want him to
respect me. obviously in a perfect world he would still be with his mom and littermates for at least another 3 weeks. unfortunately thats impossible, so i've been doing a TON of research and have been socializing him as much as possible with people and vaccinated dogs. lately i've noticed that sometimes with bigger dogs during play if they stand over him he all of a sudden freaks out (snarling, growling, biting) this is NOT play. it is aggression. my response to that thus far is to calmly try and pick him up (he DOES try to bite me when he's in one of these fits) and place him in a small quiet room for a few minutes as a "time out." I've had some people tell me i need to grab him by the scruff and very loudly say NO. I feel like doing that would just escalate the behavior.. its obviously fear based and i want to teach him how to play properly with other dogs not be even more scared.
I just really need advice on how to discipline him when he's biting people during play, how to properly deal with situations like i've described above, and really ANY and ALL advice on how to properly raise him to be a well-adjusted pitbull canine good citizen

they think he's going to be a very BIG boy, and i'm a very SMALL woman. haha.