Impreza fans questions for you.

Hi everyone, I want to learn more about old Impreza. So I have 3 questions: 1.) How do people call every gen of Impreza like first GC8 and another one? 2.) In which gen and which engine has problem with 4 cylinder? 3.) Impreza WRX version has only 2.0 liter and Impreza WRX STI has 2.5 liter?