In answer to your questions:
1. This would require the use of a plugin or modification in order to do this. You can find an ad-related plugin in the
AppThemes marketplace, however this is more for placement of more ads as opposed to the actual functionality you are looking for.
2. The sponsored ad spot you place in the settings is for the same ad, it doesn't automatically switch to other ads (again, would require a plugin or customization for this purpose)
3. Yes, you can charge separately for featured ads
4. This would require customization of the default theme on your part, but is technically possible. There is no encryption which would prevent you from making such changes.
5. There are no specific settings which would allocate ads in the way you describe so this would require customization.
6. Not by default. Explanations are as mentioned above. Thanks.