Mohammed,
Everyone learns differently. I cannot tell you how many times you have to watch the PrepCast lessons. You have to know yourself if you have understood the concepts, or if you need to view a lesson a 2nd or 3rd time to really understand it. Only you can make this decision. If you watch it once and you think "I understand this"... then go to the next lesson. But if you watch it once and you think "I did not understand this..." then watch it again.
And yes.... you should take 1 complete simulator exam every week. In this way you study (watch lessons) and then you practice (take exam). This is the most effective way of preparation.
About the Final Exam: It is an easy exam. You cannot use it to measure yourself and you have to "forget" your result. Instead: You must use The PM Exam Simulator to practice and measure yourself. In the PM Exam Simulator try and reach 75% - 80% correct in each exam.