Why is having too much fat or too little fat a potentially serious health problem

There are many reasons but one is,

Being too fat is a problem because if you eat too much, certain types of fat can cause a diet rich in saturated fat which can make cholesterol levels in blood. That can increase risk for heart disease.

Having too little fat is a problem because you could have mood problems, heart problems, Excessive appetite and eating too many vitamins causing more health problems

the last statement is correct i.e.

when your heart is not pumping enough blood around your body because your heart is severely failing, you may need an artificial heart. an artificial heart is a mechanical device, about the size of an orange, that is connected to your heart or implanted in your chest to or replace a failing heart.

1. entire bag, then the entire bag of calories

2. the percent of fat would be the percent of fat from the serving size, added up to the entire bag of calories

3/4. the saturated fat would be on the bag label, but im pretty sure if you take the serving size and do the math to figure it out you could find out in total the fiber, saturated fat,etc..

5. no probably not