Designers don't need to upload files, just provide download links.
2) Once a file is approved the product is manually added to the website and each designer must have access to a little designer panel where they can see the amount of sales for their products, date, income, etc...
3) Each sale generates 30% commission to the owner.
4) The designer has a "withdraw" button that is NOT automatically, just need to reset the income and send a mail to the admin.
That's it :)