Question

Could you confirm me that:

• Flex 4 is compatible and only compatible with Flash 10
• Flex 3 is compatible and only compatible with Flash 9 & 10

Answer 1

Flex 4 requires Flash player 10

Excerpts from the linked page:

you can open the <Flex SDK>/framework/flex-config.xml file for an SDK build and it should tell you what the minimum required Player version is for that particular SDK:

<flex-config>
  <!-- Specifies the minimum player version that will run the compiled SWF. -->
  <target-player>10.0.0</target-player>

  <!-- other tags -->
</flex-config>

You can use this to find the min-version required for Flex-3 also; This post on SO says you need Flash Player 9 or above to run it.