How Much Fat Do I Need?
What is the optimal amount of fat I need every day?
What kind of criteria do I use to determine the right amount of fat intake?
You experiment. For some people more fat is definitely what they need and it forms the basis of their diet. For other people they feel better on more carbs and fat is less a part of their diets.
Nutrition is individual and there is NO single recommendation anyone can make that would be right for everyone. The "optimal" amount needed is the level where you personally feel best. Experiment, experiment, experiment.