Can someone please guide me with the correct reason and approach for the below points.

1. What's the advantage of Power Apps over traditional Dynamics CRM

2. When we say "Dynamics 365 customer engagement", do we mean CRM v9.0 or above

3. Is the traditional development method still valid for PowerApp development?

4. If someone is working in a lower version of CRM, what are the methods to upgrade himself/herself so that he/she can work in the latest versions easily?

5. In the trial instances how to use the Microsoft flow

6. Is there any significant difference between the online and on-Premise CRM for v9.0