Question about design

I got some questions in my mind someday last week. I am asking myself day and night, but I cannot get any answer for some of them. Can you discuss it with me?

How much functional aspect should be involved in an interface design, and how much aesthetic?

What kind of relationships exist between simple, beautiful, easy to use, easy to learn, user friendly, user-centered, efficient, effective...?

I believe that if I can do something efficiently, that means effective, right? What is the difference between efficient and effective when we talk about a design?

Usability is very important for a design, but how much more a design should include except usability?

How a design process different with a science research process?