Sanjeev,
Here are my answers for you:
1.) You must read the PMBOK Guide at least twice because 75% of the exam comes from this book. The PrepCast does not take away this obligation.
2.) 10-12 weeks. We recommend that you watch the PrepCast and read the appropriate chapter in the PMBOK Guide "in parallel". Study about 2-3 hours every day like that.
3.) Yes. You can take the exam as often as you need. 85% of our students pass it in their first attempt. You can retake the exam immediately, however, you will see different questions.