So considering what this satan dude can do or does (allegedly) which is supposedly is to "kill and devour," it's quite embarrassing of bible-god to "allow" him to terrorize the planet - for what???

It's not necessarily for you to understand. You either accept it or reject it. Chances are that even IF you tried, the concepts would be too profound for your tiny mind to grasp. That's why there's such a thing as FAITH. If you don't subscribe to that, then can't help you friend.

So I am to expect that the child, lying in a hospital bed racked in extreme pain and dying from some incurable disease is part of some "divine plan' in which satan plays a role to "learn somebody a lesson?" Who can I pin the responsibility on? God? Satan? Both? They work together? Frightening don't you think?