Welcome to the forum!
Ive only been bite or struck at by baby BPs.
And they were defensive bites, felt like someone stabbing you quickly with a few toothpicks, it broke the skin but barely. Id rate it at a 1-2
You gotta remember when you open a tank your huge hand is coming at them from above. To a snake that lives on the ground they automatically think predator. To make less risk of getting struck at its a good idea to move slowly and to scoop the animal from under the belly, rather then grasping it from the back side. It really depends on the snake and how you approach it most of the time.
Ive never been bite or struck at by an adult BP however and I dont want to.

I had cornsnakes before I ever got a BP and I gotta say both are great pets.
BPs can be very picky eaters and I would suggest getting him converting to frozen thawed prey as quickly as you can. Its not COOL to feed a snake live, a rodent can seriously injure a snake by biting.
As far as big box pet stores go, I wouldnt NOT reccomend them. I used to work for a few months at a petsmart and its not good.
If you DO decide to buy your snake there however, make sure you tell them to show you the last time in the log book that the snake ate. Its very important to know that the snake has eaten recently because the snakes that come in from the breeders (mind you these are HUGE facitilies that supply large pet stores) they feed live. When they get to petsmart they are automatically switched to frozen thawed, whether they eat or not. If the snake choses not to eat the f/t, they just dont eat. Because petsmart doesnt "believe" in using rodents as prey items. They would rather see the snake die then feed it a live pinky. (Yet they choose to have "feeder" goldfish)
Anyways going with a breeder is a much safer option of knowing what your getting in a snake. And they can ship the animal right to your door! And most breeders are willing to answer any questions you may have. I suggest looking on kingsnake.com or faunaclassifieds.com or this site even has a classifieds section.
You picked a good forum to join
I wish you luck with your snake research. Hope we've helped you.