I'm not an expert, but I'll give you my input.
1. They are much smaller than regular rats, but big rats are often too big for many ball pythons in my opinion. The adults I have weigh 70-90g each. So, on the smaller side but not too bad.
2. Mine aren't aggressive at all. I don't pick them up and play with them, I just pet them with the back of my hand. I have not been bitten, but I try to be smart about when I go in there and mess with them. I don't handle them if I don't have to.
3. They do fine on the same food as rats. I do the crickets and super worms as occasional extras. They will also eat some fruits and veggies.
Beware though, they love to chew!! Give them plenty of stuff to chew on. Also, they will use a wheel til the end of time. The run like it is their duty in life.