Bulimia Nervosa does not guarantee weight loss. That is why most individuals with Bulimia Nervosa are either a normal weight or overweight. So the times of week varies and depends on the person and if it even works (which is not always likely). Also you do not throw up all of your food. You still absorb/consume over half of what you eat.

I will not give you an answer on how to throw up as it is dangerous for you and everyone else who sees your project.

It happens for a number of reasons. Feelings of being out of control, body image issues, traumatizing past, etc. It depends on the person.

It depends on the person if they feel hungry.

For your project talk more about how Bulimia Nervosa can kill you and damage your health permanently rather than any unlikely weight loss. Talk about how you will deal with rotting teeth, being weak/tired all the time, blue/brittle nails, yellow/gray-ish skin, malnutrition and dehydration, your esophagus tearing, irregular heartbeat, brittle bones, organ failure, depression, and more.

And most importantly emphasize that Bulimia Nervosa is NOT A CHOICE.