When you are looking for a license which forces some people to pay you but not others, you aren't looking for an open source license. The open source definition says:
No Discrimination Against Persons or Groups
The license must not discriminate against any person or group of persons.
No Discrimination Against Fields of Endeavor
The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.
That means we can not help you to find a license which does this, because that would be off-topic on this website.
But there might be a way to reach the goal you want while still keeping the project open source: dual licensing.
This is a business model used by many open source companies. Offer the software under two different licenses:
- Gratis under a copyleft license like the GPL
- For money under a proprietary license
In theory, both license models are available to anyone. But the commercial deal should include some additional perks which are important for large companies but secondary for private people and small businesses, like:
- A support contract
- A warranty
- Additional components which are not GPL and help to integrate the software in a business IT infrastructure.
- Permission to use the software in closed-source applications
The exact details of the deal (like pricing structure and whether to charge by use, by user, by cpu or whatever) are a business decision we can not really help you with unless we know your product and your market. Look at your potential customers and ask yourself what kind of deal would be acceptable when you were in their shoes. Also look at competing products and try to offer a slightly better deal than them.
Regarding your question about older versions: The older versions are out there under the MIT license. The MIT license has no revocation clause. That means the old versions stay out there under MIT and can still be changed and redistributed. There is not much you can do about it. But you will have a great competitive advantage against them: MIT licensed code can be integrated into GPL projects, but not the other way around. That means when anyone adds any new features or bugfixes to the old MIT version, you can take them and integrate them into the GPL version. But the GPL does not allow the opposite, so they can not integrate your updates into their version (unless they also switch to the GPL).
