Hi,

First scenario
- this can be done using the e-product (you will need to modify the page for downloading the product to actually make it a video play page).

Second scenario
- The credit purchase will be a separate action, e.g. implemented using an e-product or handled via a special product, that will cause the credit to be raised after successfull payment.
- The products can be uploaded by other users using a custom web part set or using the User contributions module features (I guess you're aiming for the live site, right?)
- As soon as the products are properly added to the system, they can be purchased by other customers - companies.

If you have any further questions about the possible implementation and about more details, feel free to ask.

Regards,
Zdenek