When active outside of the enclosure, that is totally normal. If they start flailing, then you have a problem.

Its a good sign of stress (in the enclosure) if the are active 24/7 inside the enclosure. It is a good sign that something with the husbandry is off. I would not say this is ALWAYS the case. Also, again in the enclosure, if your BP is active a couple days before feeding day, well, most likely she is just hungry. As you get to know your ball python more, you will begin to understand when she is stressed or just has energy to burn off.

You will figure it out. Ball pythons (or all snakes) are hard to read, not having facial expression or make noises besides hissing you really need to learn your BPs body language. Hissing often then not doesn't mean stress. I have a few snakes who will hiss when I go to pick them up, but are sweet hearts.

The key to making sure your BP is not stressed when handled is to not bring it to an area that is super busy. A few people are okay, but too many can be stressful. Also, making sure you support her body with both hands. Letting her dangle over one handle is putting a lot of pressure on one area of the body, and I could not imagine that that would be comfortable. And also watch the head and tail. Those are very sensitive points for most BPs. The more the head is touched or comes in close contact, it freaks them out.