That cage is about the equivalent to an 18 gallon. Since it is a little bit tall, there isn't that much floor space. I think it would be fine for an adult male, but an adult female would need more floor space.

If you find that your snake is a little cramped when it is older, you could always move him/her to a tub. Cheap, easy to clean, and great for humidity

There is no specific growth rate for ball pythons. They all grow at different rates. Some will eat a lot and grow slowly, some will eat very little and grow quickly. It doesn't always depend on how much they are fed.

A hatchling should be started on hopper mice for the first few feedings and then move to small adult mice. A few months after that, a full grown mouse will do. After my snakes out grow two mice per feeding, I move them to weaned rats. Once they are adults, they get small rats.

I feed 10-15% of the snakes body weight until they reach 1500g, then I just give them a small rat every week.